first missing positive integer in an array using javascript?

Question

I am trying to find missing positive integer in an. array.I don't know where my function not working ?

question given

Given an unsorted integer array, find the first missing positive integer.

Given [1,2,0] return 3,
[3,4,-1,1] return 2,
[-8, -7, -6] returns 1

my function works on following above cases works fine..

let firstMissingPositive = function(A){
 if(A.length === 1 && A[0] < 0){
 return 1
 }
 let j=0;
 for (let i = 0; i < A.length; i++) {
 if(A[i] < 0){
 let temp = A[j]
 A[j] = A[i]
 A[i] = temp;
 j++;
 }
 }
 let arr =A.slice(j);
 for (let i = 0; i < arr.length; i++) {
 if (arr[(arr[i]) - 1] > 0) {
 arr[(arr[i]) - 1] = -arr[(arr[i]) - 1]
 }
 }
 let k=0;
 while (true){
 if(arr[k]>0 || k >= arr.length){
 break;
 }
 k++
 }
 return ++k
}

**but fails in this case ** when input is this.

[ 463, 127, 436, 72, 79, 301, 613, 898, 675, 960, 832, 486, 453, 274, 133, 721, 750, 538, 545, 112, 414, 817, 885, 812, 906, 577, 544, 101, 165, 45, 489, 503, 479, 293, 234, 427, 347, 851, 316, 827, 209, 578, 255, 56, 608, 914, 156, 537, 870, 567, 284, 240, 292, 111, 590, 713, 110, 768, 598, 879, 980, 660, 46, 320, 410, 869, 154, 970, 836, 423, 413, 501, 782, 403, 561, 117, 624, 638, 67, 646, 917, 379, 344, 543, 978, 506, 936, 947, 645, 633, 375, 706, 531, 470, 551, 632, 536, 642, 573, 705, 823, 897, 26, 476, 139, 496, 628, 91, 725, 570, 701, 244, 935, 126, 2, 560, 726, 20, 680, 7, 888, 183, 80, 804, 729, 583, 728, 515, 644, 774, 856, 192, 386, 25, 57, 471, 482, 174, 627, 757, 714, 203, 206, 847, 245, 336, 989, 326, 607, 95, 69, 71, 54, 975, 366, 591, 185, 964, 848, 84, 819, 737, 687, 215, 904, 651, 289, 134, 232, 341, 932, 64, 483, 128, 901, 808, 896, 941, 530, 195, 865, 903, 472, 508, 42, 971, 53, 86, 689, 925, 685, 934, 549, 841, 169, 317, 826, 600, 950, 90, 495, 219, 674, 814, 359, 556, 269, 187, 517, 541, 558, 8, 744, 958, 332, 163, 862, 218, 376, 23, 321, 346, 534, 864, 157, 285, 318, 200, 595, 810, 43, 32, 368, 753, 670, 887, 238, 1000, 513, 979, 499, 708, 473, 584, 981, 106, 695, 868, 881, 610, 273, 239, 190, 281, 373, 247, 364, 396, 837, 521, 871, 528, 617, 123, 894, 965, 108, 976, 451, 454, 673, 910, 681, 300, 702, 703, 307, 196, 535, 407, 763, 966, 945, 944, 65, 752, 776, 973, 554, 3, 998, 559, 35, -3, 147, 395, 761, 442, 586, 899, 191, 990, 606, 771, 393, 649, 987, 593, 877, 527, 201, 259, 150, 683, 263, 330, 21, 105, 406, 233, 303, 254, 33, 417, 497, 622, 286, 9, 967, 603, 78, 118, 304, 235, 985, 657, 741, 425, 995, 592, 844, 933, 99, 524, 418, 623, 529, 797, 342, 217, 580, 691, 772, 13, 390, 666, 87, 448, 505, 907, 765, 802, 484, 419, 669, 780, 96, 585, 796, 686, 302, 858, 388, 438, 893, 735, 360, 913, 902, 279, 720, 408, 287, 996, 507, 28, 416, 731, 928, 977, 547, 739, 788, 168, 331, 146, 664, 619, 723, 732, 102, 14, 424, 216, 575, 568, 93, 992, 272, 160, 389, 47, 647, 189, 988, 343, 991, 940, 358, 181, 611, 229, 265, 892, 422, 211, 443, 747, 736, 266, 652, 351, 612, 514, 876, 637, 329, 474, 68, 730, 825, 676, 778, 208, 956, 270, 398, 968, 268, 594, 288, 385, 866, 197, 428, 441, 672, 158, 618, 811, 363, 905, 462, 241, 226, 450, 309, 170, 822, 727, 333, 335, 92, 540, 202, 205, 115, 153, 569, 142, 290, 943, 394, 248, 228, 643, 415, 784, 579, 571, 291, 177, 711, 149, 130, 921, 922, 439, 951, 338, 769, 283, 308, 857, 253, 833, 490, 824, 518, 525, 131, 924, 27, 830, 915, 237, 694, 581, 609, 19, 152, 566, 465, 140, 81, 313, 969, 327, 6, 526, 135, 186, 656, 662, 155, 874, 648, 488, 199, 677, 952, 614, 722, 369, 682, 129, 478, 433, 809, 891, 717, 550, 748, 0, 323, 469, 151, 41, 299, 193, 487, 931, 634, 400, 799, 884, 405, 480, 76, 805, 926, 426, 312, 821, 178, 789, 449, 697, 853, 295, 48, 224, 397, 447, 946, 49, 382, 236, 867, 485, 349, 231, 227, 39, 38, 882, 210, 457, 222, 852, 665, 138, 455, 114, 204, 498, 511, 230, 509, 278, 365, 831, 412, 5, 816, 1, 324, 194, 464, 141, 420, 795, 839, 641, 10, 777, 15, 519, 829, 961, 109, 31, -5, 63, 421, 77, 430, 542, 452, 256, 355, 357, 704, 434, 459, 262, 132, 863, 468, 929, 716, 564, 890, 616, 855, 845, 548, 143, 145, 707, 787, 948, 11, 872, 61, 909, 762, 639, 786, 350, 136, 972, 75, 605, 354, 339, 305, 754, 755, 658, 40, 319, 620, 679, 984, 252, 477, 432, 684, 766, 280, 912, 949, 328, 834, 522, 310, 920, 546, 770, 214, 962, 678, 760, 916, -4, 401, 12, 957, 806, 791, 261, 277, 372, 17, 85, 982, 97, 125, 698, 399, 381, 655, 315, 182, 923, 886, 440, 223, 387, 173, 663, 588, 122, 113, 98, 803, 353, 668, 311, 587, 444, 636, 939, 429, 790, 718, 938, 738, 50, 362, 435, 813, 908, 650, 843, 959, 460, 849, 167, 384, 348, 467, 337, 356, 724, 516, 121, 880, 667, 779, 709, 986, 751, 51, 781, 659, 794, 653, 635, 553, 60, 322, 352, 696, 392, 250, 119, 431, 746, 164, 107, 563, 461, 532, 712, 391, 840, 380, 801, 574, 900, 576, 640, 378, 963, 601, 267, 207, 370, 225, 260, 500, 883, 159, 58, 166, 745, 179, 251, 271, 294, 257, 631, 895, 604, 828, 953, 520, 16, 818, 539, 491, 120, 875, 89, 692, 458, 552, 599, 861, 492, 74, 699, 55, 475, 345, 24, 700, 889, 937, 785, 758, 983 ]

expected output is 4

and my output is 1

here is my code https://jsbin.com/poduqayime/2/edit?html,js,console,output

• Ilijanovic: i am not sure but i guess you are wrong here, you should go to codereview.stackexchange.com
• nice_dev: @Ifaruki If the OP looks for a cleaner solution, then codereview suits best. If something doesn't work, putting on SO is on topic.
• EugenSunic: please reduce you sample array size when posting a question
• nice_dev: @EugenSunic That's the case it fails for.
• samgak: Does your algorithm handle the case where there are duplicate values in the array?

Answer 1

// finding first missing +VE in javascript array
const firstMissingPositive = (arr=[]) => {for(i=1; ; i++) if(arr.indexOf(i) == -1) return i;}

// finding first missing +VE in javascript array
const firstMissingPositive = (arr=[]) => {for(i=1; ; i++) if(arr.indexOf(i) == -1) return i;}
let firstArr = [1,2,0]
console.log(`In firstArr missed : ${firstMissingPositive(firstArr)}`)
let secondArr = [3,4,-1,1]
console.log(`In secondArr missed : ${firstMissingPositive(secondArr)}`)
let thirdArr = [-8, -7, -6]
console.log(`In thirdArr missed : ${firstMissingPositive(thirdArr)}`)
let yourArr = [ 463, 127, 436, 72, 79, 301, 613, 898, 675, 960, 832, 486, 453, 274, 133, 721, 750, 538, 545, 112, 414, 817, 885, 812, 906, 577, 544, 101, 165, 45, 489, 503, 479, 293, 234, 427, 347, 851, 316, 827, 209, 578, 255, 56, 608, 914, 156, 537, 870, 567, 284, 240, 292, 111, 590, 713, 110, 768, 598, 879, 980, 660, 46, 320, 410, 869, 154, 970, 836, 423, 413, 501, 782, 403, 561, 117, 624, 638, 67, 646, 917, 379, 344, 543, 978, 506, 936, 947, 645, 633, 375, 706, 531, 470, 551, 632, 536, 642, 573, 705, 823, 897, 26, 476, 139, 496, 628, 91, 725, 570, 701, 244, 935, 126, 2, 560, 726, 20, 680, 7, 888, 183, 80, 804, 729, 583, 728, 515, 644, 774, 856, 192, 386, 25, 57, 471, 482, 174, 627, 757, 714, 203, 206, 847, 245, 336, 989, 326, 607, 95, 69, 71, 54, 975, 366, 591, 185, 964, 848, 84, 819, 737, 687, 215, 904, 651, 289, 134, 232, 341, 932, 64, 483, 128, 901, 808, 896, 941, 530, 195, 865, 903, 472, 508, 42, 971, 53, 86, 689, 925, 685, 934, 549, 841, 169, 317, 826, 600, 950, 90, 495, 219, 674, 814, 359, 556, 269, 187, 517, 541, 558, 8, 744, 958, 332, 163, 862, 218, 376, 23, 321, 346, 534, 864, 157, 285, 318, 200, 595, 810, 43, 32, 368, 753, 670, 887, 238, 1000, 513, 979, 499, 708, 473, 584, 981, 106, 695, 868, 881, 610, 273, 239, 190, 281, 373, 247, 364, 396, 837, 521, 871, 528, 617, 123, 894, 965, 108, 976, 451, 454, 673, 910, 681, 300, 702, 703, 307, 196, 535, 407, 763, 966, 945, 944, 65, 752, 776, 973, 554, 3, 998, 559, 35, -3, 147, 395, 761, 442, 586, 899, 191, 990, 606, 771, 393, 649, 987, 593, 877, 527, 201, 259, 150, 683, 263, 330, 21, 105, 406, 233, 303, 254, 33, 417, 497, 622, 286, 9, 967, 603, 78, 118, 304, 235, 985, 657, 741, 425, 995, 592, 844, 933, 99, 524, 418, 623, 529, 797, 342, 217, 580, 691, 772, 13, 390, 666, 87, 448, 505, 907, 765, 802, 484, 419, 669, 780, 96, 585, 796, 686, 302, 858, 388, 438, 893, 735, 360, 913, 902, 279, 720, 408, 287, 996, 507, 28, 416, 731, 928, 977, 547, 739, 788, 168, 331, 146, 664, 619, 723, 732, 102, 14, 424, 216, 575, 568, 93, 992, 272, 160, 389, 47, 647, 189, 988, 343, 991, 940, 358, 181, 611, 229, 265, 892, 422, 211, 443, 747, 736, 266, 652, 351, 612, 514, 876, 637, 329, 474, 68, 730, 825, 676, 778, 208, 956, 270, 398, 968, 268, 594, 288, 385, 866, 197, 428, 441, 672, 158, 618, 811, 363, 905, 462, 241, 226, 450, 309, 170, 822, 727, 333, 335, 92, 540, 202, 205, 115, 153, 569, 142, 290, 943, 394, 248, 228, 643, 415, 784, 579, 571, 291, 177, 711, 149, 130, 921, 922, 439, 951, 338, 769, 283, 308, 857, 253, 833, 490, 824, 518, 525, 131, 924, 27, 830, 915, 237, 694, 581, 609, 19, 152, 566, 465, 140, 81, 313, 969, 327, 6, 526, 135, 186, 656, 662, 155, 874, 648, 488, 199, 677, 952, 614, 722, 369, 682, 129, 478, 433, 809, 891, 717, 550, 748, 0, 323, 469, 151, 41, 299, 193, 487, 931, 634, 400, 799, 884, 405, 480, 76, 805, 926, 426, 312, 821, 178, 789, 449, 697, 853, 295, 48, 224, 397, 447, 946, 49, 382, 236, 867, 485, 349, 231, 227, 39, 38, 882, 210, 457, 222, 852, 665, 138, 455, 114, 204, 498, 511, 230, 509, 278, 365, 831, 412, 5, 816, 1, 324, 194, 464, 141, 420, 795, 839, 641, 10, 777, 15, 519, 829, 961, 109, 31, -5, 63, 421, 77, 430, 542, 452, 256, 355, 357, 704, 434, 459, 262, 132, 863, 468, 929, 716, 564, 890, 616, 855, 845, 548, 143, 145, 707, 787, 948, 11, 872, 61, 909, 762, 639, 786, 350, 136, 972, 75, 605, 354, 339, 305, 754, 755, 658, 40, 319, 620, 679, 984, 252, 477, 432, 684, 766, 280, 912, 949, 328, 834, 522, 310, 920, 546, 770, 214, 962, 678, 760, 916, -4, 401, 12, 957, 806, 791, 261, 277, 372, 17, 85, 982, 97, 125, 698, 399, 381, 655, 315, 182, 923, 886, 440, 223, 387, 173, 663, 588, 122, 113, 98, 803, 353, 668, 311, 587, 444, 636, 939, 429, 790, 718, 938, 738, 50, 362, 435, 813, 908, 650, 843, 959, 460, 849, 167, 384, 348, 467, 337, 356, 724, 516, 121, 880, 667, 779, 709, 986, 751, 51, 781, 659, 794, 653, 635, 553, 60, 322, 352, 696, 392, 250, 119, 431, 746, 164, 107, 563, 461, 532, 712, 391, 840, 380, 801, 574, 900, 576, 640, 378, 963, 601, 267, 207, 370, 225, 260, 500, 883, 159, 58, 166, 745, 179, 251, 271, 294, 257, 631, 895, 604, 828, 953, 520, 16, 818, 539, 491, 120, 875, 89, 692, 458, 552, 599, 861, 492, 74, 699, 55, 475, 345, 24, 700, 889, 937, 785, 758, 983 ]
console.log(`In yourArr missed : ${firstMissingPositive(yourArr)}`)

• greybeard: This does not answer where my function not working ? It gets avoidably slow for higher results.
• Shahzad Harim: what may be max length of your array ?
• user944513: @ShahzadHarim indexof seach in whole array
• nice_dev: Your solution is O(n^2).

Answer 2

Simple and easy solution using ES6 syntax Set

const firstMissingPositive = function(nums) {
 const set = new Set(nums);
 let min = 1;
 
 while(set.has(min)) {
 min++
 }
 return min
};
firstMissingPositive([1,2,0]) // returns 3

• Vladimir B.: I like that! Applied it on a simple task of mine, thank you pal.

Answer 3

 if (arr[(arr[i]) - 1] > 0) {
 arr[(arr[i]) - 1] = -arr[(arr[i]) - 1]
 }

Above code creates the issue. Here, it's quite possible that the current arr[i] was already made negative by some other index. So, (arr[i]) - 1 would yield an even negative index. So, to solve this, you need to use absolute value using Math.abs().

---

You also have if(A[i] < 0){ in your first for loop. It's better to have it as if(A[i] <= 0){ as we don't care about non negative integer as well.

---

Your while loop has the condition if(arr[k]>0 || k >= arr.length){. It should rather be the other way round like if(k == arr.length || arr[k] > 0){

---

Overall, your code would look like below:

let firstMissingPositive = function(A) {
 let j = 0;
 for (let i = 0; i < A.length; i++) {
 if (A[i] <= 0) {
 let temp = A[j]
 A[j] = A[i]
 A[i] = temp;
 j++;
 }
 }
 let arr = A.slice(j);
 for (let i = 0; i < arr.length; i++) {
 if (arr[Math.abs(arr[i]) - 1] > 0) {
 arr[Math.abs(arr[i]) - 1] = -arr[Math.abs(arr[i]) - 1]
 }
 }
 let k = 0;
 while (true) {
 if (k == arr.length || arr[k] > 0) {
 break;
 }
 k++
 }
 return ++k
}
console.log(firstMissingPositive([463, 127, 436, 72, 79, 301, 613, 898, 675, 960, 832, 486, 453, 274, 133, 721, 750, 538, 545, 112, 414, 817, 885, 812, 906, 577, 544, 101, 165, 45, 489, 503, 479, 293, 234, 427, 347, 851, 316, 827, 209, 578, 255, 56, 608, 914, 156, 537, 870, 567, 284, 240, 292, 111, 590, 713, 110, 768, 598, 879, 980, 660, 46, 320, 410, 869, 154, 970, 836, 423, 413, 501, 782, 403, 561, 117, 624, 638, 67, 646, 917, 379, 344, 543, 978, 506, 936, 947, 645, 633, 375, 706, 531, 470, 551, 632, 536, 642, 573, 705, 823, 897, 26, 476, 139, 496, 628, 91, 725, 570, 701, 244, 935, 126, 2, 560, 726, 20, 680, 7, 888, 183, 80, 804, 729, 583, 728, 515, 644, 774, 856, 192, 386, 25, 57, 471, 482, 174, 627, 757, 714, 203, 206, 847, 245, 336, 989, 326, 607, 95, 69, 71, 54, 975, 366, 591, 185, 964, 848, 84, 819, 737, 687, 215, 904, 651, 289, 134, 232, 341, 932, 64, 483, 128, 901, 808, 896, 941, 530, 195, 865, 903, 472, 508, 42, 971, 53, 86, 689, 925, 685, 934, 549, 841, 169, 317, 826, 600, 950, 90, 495, 219, 674, 814, 359, 556, 269, 187, 517, 541, 558, 8, 744, 958, 332, 163, 862, 218, 376, 23, 321, 346, 534, 864, 157, 285, 318, 200, 595, 810, 43, 32, 368, 753, 670, 887, 238, 1000, 513, 979, 499, 708, 473, 584, 981, 106, 695, 868, 881, 610, 273, 239, 190, 281, 373, 247, 364, 396, 837, 521, 871, 528, 617, 123, 894, 965, 108, 976, 451, 454, 673, 910, 681, 300, 702, 703, 307, 196, 535, 407, 763, 966, 945, 944, 65, 752, 776, 973, 554, 3, 998, 559, 35, -3, 147, 395, 761, 442, 586, 899, 191, 990, 606, 771, 393, 649, 987, 593, 877, 527, 201, 259, 150, 683, 263, 330, 21, 105, 406, 233, 303, 254, 33, 417, 497, 622, 286, 9, 967, 603, 78, 118, 304, 235, 985, 657, 741, 425, 995, 592, 844, 933, 99, 524, 418, 623, 529, 797, 342, 217, 580, 691, 772, 13, 390, 666, 87, 448, 505, 907, 765, 802, 484, 419, 669, 780, 96, 585, 796, 686, 302, 858, 388, 438, 893, 735, 360, 913, 902, 279, 720, 408, 287, 996, 507, 28, 416, 731, 928, 977, 547, 739, 788, 168, 331, 146, 664, 619, 723, 732, 102, 14, 424, 216, 575, 568, 93, 992, 272, 160, 389, 47, 647, 189, 988, 343, 991, 940, 358, 181, 611, 229, 265, 892, 422, 211, 443, 747, 736, 266, 652, 351, 612, 514, 876, 637, 329, 474, 68, 730, 825, 676, 778, 208, 956, 270, 398, 968, 268, 594, 288, 385, 866, 197, 428, 441, 672, 158, 618, 811, 363, 905, 462, 241, 226, 450, 309, 170, 822, 727, 333, 335, 92, 540, 202, 205, 115, 153, 569, 142, 290, 943, 394, 248, 228, 643, 415, 784, 579, 571, 291, 177, 711, 149, 130, 921, 922, 439, 951, 338, 769, 283, 308, 857, 253, 833, 490, 824, 518, 525, 131, 924, 27, 830, 915, 237, 694, 581, 609, 19, 152, 566, 465, 140, 81, 313, 969, 327, 6, 526, 135, 186, 656, 662, 155, 874, 648, 488, 199, 677, 952, 614, 722, 369, 682, 129, 478, 433, 809, 891, 717, 550, 748, 0, 323, 469, 151, 41, 299, 193, 487, 931, 634, 400, 799, 884, 405, 480, 76, 805, 926, 426, 312, 821, 178, 789, 449, 697, 853, 295, 48, 224, 397, 447, 946, 49, 382, 236, 867, 485, 349, 231, 227, 39, 38, 882, 210, 457, 222, 852, 665, 138, 455, 114, 204, 498, 511, 230, 509, 278, 365, 831, 412, 5, 816, 1, 324, 194, 464, 141, 420, 795, 839, 641, 10, 777, 15, 519, 829, 961, 109, 31, -5, 63, 421, 77, 430, 542, 452, 256, 355, 357, 704, 434, 459, 262, 132, 863, 468, 929, 716, 564, 890, 616, 855, 845, 548, 143, 145, 707, 787, 948, 11, 872, 61, 909, 762, 639, 786, 350, 136, 972, 75, 605, 354, 339, 305, 754, 755, 658, 40, 319, 620, 679, 984, 252, 477, 432, 684, 766, 280, 912, 949, 328, 834, 522, 310, 920, 546, 770, 214, 962, 678, 760, 916, -4, 401, 12, 957, 806, 791, 261, 277, 372, 17, 85, 982, 97, 125, 698, 399, 381, 655, 315, 182, 923, 886, 440, 223, 387, 173, 663, 588, 122, 113, 98, 803, 353, 668, 311, 587, 444, 636, 939, 429, 790, 718, 938, 738, 50, 362, 435, 813, 908, 650, 843, 959, 460, 849, 167, 384, 348, 467, 337, 356, 724, 516, 121, 880, 667, 779, 709, 986, 751, 51, 781, 659, 794, 653, 635, 553, 60, 322, 352, 696, 392, 250, 119, 431, 746, 164, 107, 563, 461, 532, 712, 391, 840, 380, 801, 574, 900, 576, 640, 378, 963, 601, 267, 207, 370, 225, 260, 500, 883, 159, 58, 166, 745, 179, 251, 271, 294, 257, 631, 895, 604, 828, 953, 520, 16, 818, 539, 491, 120, 875, 89, 692, 458, 552, 599, 861, 492, 74, 699, 55, 475, 345, 24, 700, 889, 937, 785, 758, 983]));
console.log(firstMissingPositive([1, 2, 0]));
console.log(firstMissingPositive([3, 4, -1, 1]));
console.log(firstMissingPositive([-8, -7, -6]));
console.log(firstMissingPositive([-8]));

Answer 4

The logic here is to sort the array first; then if the number is positive and not equal to previous number + 1; then you'd found the missing number :)

function findTheMissingPossitiveInt(array) {
 let missing = 1;
 array.sort((m, n) => m - n);
 array.reduce((acc, cur, i, arr) => {
 if (cur > 0) {
 if (cur != acc + 1) {
 missing = acc + 1;
 //short-circuiting reduce execution
 arr.splice(1);
 }
 }
 return cur;
 }, 0);
 return missing;
}
const a = [ 463, 127, 436, 72, 79, 301, 613, 898, 675, 960, 832, 486, 453, 274, 133, 721, 750, 538, 545, 112, 414, 817, 885, 812, 906, 577, 544, 101, 165, 45, 489, 503, 479, 293, 234, 427, 347, 851, 316, 827, 209, 578, 255, 56, 608, 914, 156, 537, 870, 567, 284, 240, 292, 111, 590, 713, 110, 768, 598, 879, 980, 660, 46, 320, 410, 869, 154, 970, 836, 423, 413, 501, 782, 403, 561, 117, 624, 638, 67, 646, 917, 379, 344, 543, 978, 506, 936, 947, 645, 633, 375, 706, 531, 470, 551, 632, 536, 642, 573, 705, 823, 897, 26, 476, 139, 496, 628, 91, 725, 570, 701, 244, 935, 126, 2, 560, 726, 20, 680, 7, 888, 183, 80, 804, 729, 583, 728, 515, 644, 774, 856, 192, 386, 25, 57, 471, 482, 174, 627, 757, 714, 203, 206, 847, 245, 336, 989, 326, 607, 95, 69, 71, 54, 975, 366, 591, 185, 964, 848, 84, 819, 737, 687, 215, 904, 651, 289, 134, 232, 341, 932, 64, 483, 128, 901, 808, 896, 941, 530, 195, 865, 903, 472, 508, 42, 971, 53, 86, 689, 925, 685, 934, 549, 841, 169, 317, 826, 600, 950, 90, 495, 219, 674, 814, 359, 556, 269, 187, 517, 541, 558, 8, 744, 958, 332, 163, 862, 218, 376, 23, 321, 346, 534, 864, 157, 285, 318, 200, 595, 810, 43, 32, 368, 753, 670, 887, 238, 1000, 513, 979, 499, 708, 473, 584, 981, 106, 695, 868, 881, 610, 273, 239, 190, 281, 373, 247, 364, 396, 837, 521, 871, 528, 617, 123, 894, 965, 108, 976, 451, 454, 673, 910, 681, 300, 702, 703, 307, 196, 535, 407, 763, 966, 945, 944, 65, 752, 776, 973, 554, 3, 998, 559, 35, -3, 147, 395, 761, 442, 586, 899, 191, 990, 606, 771, 393, 649, 987, 593, 877, 527, 201, 259, 150, 683, 263, 330, 21, 105, 406, 233, 303, 254, 33, 417, 497, 622, 286, 9, 967, 603, 78, 118, 304, 235, 985, 657, 741, 425, 995, 592, 844, 933, 99, 524, 418, 623, 529, 797, 342, 217, 580, 691, 772, 13, 390, 666, 87, 448, 505, 907, 765, 802, 484, 419, 669, 780, 96, 585, 796, 686, 302, 858, 388, 438, 893, 735, 360, 913, 902, 279, 720, 408, 287, 996, 507, 28, 416, 731, 928, 977, 547, 739, 788, 168, 331, 146, 664, 619, 723, 732, 102, 14, 424, 216, 575, 568, 93, 992, 272, 160, 389, 47, 647, 189, 988, 343, 991, 940, 358, 181, 611, 229, 265, 892, 422, 211, 443, 747, 736, 266, 652, 351, 612, 514, 876, 637, 329, 474, 68, 730, 825, 676, 778, 208, 956, 270, 398, 968, 268, 594, 288, 385, 866, 197, 428, 441, 672, 158, 618, 811, 363, 905, 462, 241, 226, 450, 309, 170, 822, 727, 333, 335, 92, 540, 202, 205, 115, 153, 569, 142, 290, 943, 394, 248, 228, 643, 415, 784, 579, 571, 291, 177, 711, 149, 130, 921, 922, 439, 951, 338, 769, 283, 308, 857, 253, 833, 490, 824, 518, 525, 131, 924, 27, 830, 915, 237, 694, 581, 609, 19, 152, 566, 465, 140, 81, 313, 969, 327, 6, 526, 135, 186, 656, 662, 155, 874, 648, 488, 199, 677, 952, 614, 722, 369, 682, 129, 478, 433, 809, 891, 717, 550, 748, 0, 323, 469, 151, 41, 299, 193, 487, 931, 634, 400, 799, 884, 405, 480, 76, 805, 926, 426, 312, 821, 178, 789, 449, 697, 853, 295, 48, 224, 397, 447, 946, 49, 382, 236, 867, 485, 349, 231, 227, 39, 38, 882, 210, 457, 222, 852, 665, 138, 455, 114, 204, 498, 511, 230, 509, 278, 365, 831, 412, 5, 816, 1, 324, 194, 464, 141, 420, 795, 839, 641, 10, 777, 15, 519, 829, 961, 109, 31, -5, 63, 421, 77, 430, 542, 452, 256, 355, 357, 704, 434, 459, 262, 132, 863, 468, 929, 716, 564, 890, 616, 855, 845, 548, 143, 145, 707, 787, 948, 11, 872, 61, 909, 762, 639, 786, 350, 136, 972, 75, 605, 354, 339, 305, 754, 755, 658, 40, 319, 620, 679, 984, 252, 477, 432, 684, 766, 280, 912, 949, 328, 834, 522, 310, 920, 546, 770, 214, 962, 678, 760, 916, -4, 401, 12, 957, 806, 791, 261, 277, 372, 17, 85, 982, 97, 125, 698, 399, 381, 655, 315, 182, 923, 886, 440, 223, 387, 173, 663, 588, 122, 113, 98, 803, 353, 668, 311, 587, 444, 636, 939, 429, 790, 718, 938, 738, 50, 362, 435, 813, 908, 650, 843, 959, 460, 849, 167, 384, 348, 467, 337, 356, 724, 516, 121, 880, 667, 779, 709, 986, 751, 51, 781, 659, 794, 653, 635, 553, 60, 322, 352, 696, 392, 250, 119, 431, 746, 164, 107, 563, 461, 532, 712, 391, 840, 380, 801, 574, 900, 576, 640, 378, 963, 601, 267, 207, 370, 225, 260, 500, 883, 159, 58, 166, 745, 179, 251, 271, 294, 257, 631, 895, 604, 828, 953, 520, 16, 818, 539, 491, 120, 875, 89, 692, 458, 552, 599, 861, 492, 74, 699, 55, 475, 345, 24, 700, 889, 937, 785, 758, 983];
const b = [-1,-7,-8];
const c = [ -2, 0,1, 2 , 7];
console.log(findTheMissingPossitiveInt(a));
console.log(findTheMissingPossitiveInt(b));
console.log(findTheMissingPossitiveInt(c));

• Mechanic: you can copy the array in the function body if mutation is a concern

Answer 5

Javascript

let firstMissingPositive = function(nums) {
 let len = nums.length;
 let tmp = 0;
 let i = 0;
 while (i < len) {
 tmp = nums[i];
if (tmp > 0 && tmp !== i + 1 && tmp !== nums[tmp - 1]) swap(nums, i,tmp - 1);
 else i++;
 }
 for (var j = 0; j < len; j++) {
 if (nums[j] !== j + 1) return j + 1;
 }
 return len + 1;
};
let swap = function (arr, i, j) {
 let tmp = arr[i];
 arr[i] = arr[j];
 arr[j] = tmp;
};

• Scott Sauyet: Welcome to StackOverflow. Please don't post code-only answers. Please edit to add some context and explanations.