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Commit cfbce0e

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新增题解
1 parent 9419280 commit cfbce0e

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34 files changed

+311
-518
lines changed

34 files changed

+311
-518
lines changed

‎README.md‎

Lines changed: 70 additions & 70 deletions
Large diffs are not rendered by default.

‎codes/java/leetcodes/src/main/java/com/hit/basinfo/sort_algorithm/QuickSort.java‎

Lines changed: 2 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -14,9 +14,7 @@ public class QuickSort {
1414
*/
1515
public void quickSort(int[] nums) {
1616
// check parameters
17-
if (nums == null || nums.length < 2) {
18-
return;
19-
}
17+
if (nums == null || nums.length < 2) return;
2018
// initial value
2119
int left = 0, right = nums.length - 1;
2220
// call overload method
@@ -32,13 +30,9 @@ public void quickSort(int[] nums) {
3230
*/
3331
private void quickSort(int[] nums, int left, int right) {
3432
// check parameters
35-
if (nums == null || nums.length < 2) {
36-
return;
37-
}
38-
33+
if (nums == null || nums.length < 2) return;
3934
// obtain the division datum point, which is the left value after the division
4035
int index = partition(nums, left, right);
41-
4236
// sort left half
4337
if (left < index - 1) {
4438
quickSort(nums, left, index - 1);
@@ -60,7 +54,6 @@ private void quickSort(int[] nums, int left, int right) {
6054
private int partition(int[] nums, int left, int right) {
6155
// the position in the middle of the default array is the reference point
6256
int pivot = nums[(left + right) / 2];
63-
6457
/**
6558
* when left < = right, the cycle condition is satisfied
6659
* when left > right, it means that the current trip is completed
@@ -74,7 +67,6 @@ private int partition(int[] nums, int left, int right) {
7467
while (nums[right] > pivot) {
7568
right--;
7669
}
77-
7870
// find the elements that meet the conditions and exchange them
7971
if (left <= right) {
8072
// exchange element

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/easy_collection/array/_48.java‎

Lines changed: 7 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -51,15 +51,14 @@
5151
*/
5252
public class _48 {
5353
public void rotate(int[][] matrix) {
54-
int s = 0, e = matrix.length - 1;
55-
while (s < e) {
56-
int[] temp = matrix[s];
57-
matrix[s] = matrix[e];
58-
matrix[e] = temp;
59-
s++;
60-
e--;
54+
int start = 0, end = matrix.length - 1;
55+
while (start < end) {
56+
int[] temp = matrix[start];
57+
matrix[start] = matrix[end];
58+
matrix[end] = temp;
59+
start++;
60+
end--;
6161
}
62-
6362
for (int i = 0; i < matrix.length; i++) {
6463
for (int j = i + 1; j < matrix[i].length; j++) {
6564
int temp = matrix[i][j];

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/easy_collection/dynamic_programming/_121.java‎

Lines changed: 0 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -25,20 +25,7 @@
2525
* Explanation: In this case, no transaction is done, i.e. max profit = 0.
2626
*/
2727
public class _121 {
28-
2928
public int maxProfit(int[] prices) {
30-
int maxProfit = 0;
31-
for (int i = 0; i < prices.length - 1; i++) {
32-
for (int j = i + 1; j < prices.length; j++) {
33-
int profit = prices[j] - prices[i];
34-
if (profit > maxProfit)
35-
maxProfit = profit;
36-
}
37-
}
38-
return maxProfit;
39-
}
40-
41-
public int maxProfit2(int[] prices) {
4229
int minPrice = Integer.MAX_VALUE;
4330
int maxProfit = 0;
4431
for (int price : prices) {

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/easy_collection/dynamic_programming/_198.java‎

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -25,11 +25,12 @@
2525
*/
2626
public class _198 {
2727
public int rob(int[] nums) {
28-
int[][] dp = new int[nums.length + 1][2];
29-
for (int i = 1; i <= nums.length; i++) {
30-
dp[i][0] = Math.max(dp[i - 1][0], dp[i - 1][1]);
31-
dp[i][1] = nums[i - 1] + dp[i - 1][0];
28+
int prevMax = 0, currMax = 0;
29+
for (int n : nums) {
30+
int temp = currMax;
31+
currMax = Math.max(prevMax + n, currMax);
32+
prevMax = temp;
3233
}
33-
return Math.max(dp[nums.length][0], dp[nums.length][1]);
34+
return currMax;
3435
}
3536
}

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/easy_collection/math/_13.java‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -52,7 +52,7 @@
5252
*/
5353
public class _13 {
5454
public int romanToInt(String s) {
55-
intnums[] = new int[s.length()];
55+
int[] nums = new int[s.length()];
5656
for (int i = 0; i < s.length(); i++) {
5757
switch (s.charAt(i)) {
5858
case 'M':
@@ -80,10 +80,11 @@ public int romanToInt(String s) {
8080
}
8181
int sum = 0;
8282
for (int i = 0; i < nums.length - 1; i++) {
83-
if (nums[i] < nums[i + 1])
83+
if (nums[i] < nums[i + 1]) {
8484
sum -= nums[i];
85-
else
85+
} else {
8686
sum += nums[i];
87+
}
8788
}
8889
return sum + nums[nums.length - 1];
8990
}

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/easy_collection/math/_412.java‎

Lines changed: 1 addition & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -39,12 +39,9 @@ public class _412 {
3939
public List<String> fizzBuzz(int n) {
4040
// ans list
4141
List<String> ans = new ArrayList<String>();
42-
4342
for (int num = 1; num <= n; num++) {
44-
4543
boolean divisibleBy3 = (num % 3 == 0);
4644
boolean divisibleBy5 = (num % 5 == 0);
47-
4845
if (divisibleBy3 && divisibleBy5) {
4946
// Divides by both 3 and 5, add FizzBuzz
5047
ans.add("FizzBuzz");
@@ -59,78 +56,63 @@ public List<String> fizzBuzz(int n) {
5956
ans.add(Integer.toString(num));
6057
}
6158
}
62-
6359
return ans;
6460
}
6561

6662
public List<String> fizzBuzz2(int n) {
6763
// ans list
6864
List<String> ans = new ArrayList<String>();
69-
7065
for (int num = 1; num <= n; num++) {
71-
7266
boolean divisibleBy3 = (num % 3 == 0);
7367
boolean divisibleBy5 = (num % 5 == 0);
74-
7568
String numAnsStr = "";
76-
7769
if (divisibleBy3) {
7870
// Divides by 3, add Fizz
7971
numAnsStr += "Fizz";
8072
}
81-
8273
if (divisibleBy5) {
8374
// Divides by 5, add Buzz
8475
numAnsStr += "Buzz";
8576
}
86-
8777
if (numAnsStr.equals("")) {
8878
// Not divisible by 3 or 5, add the number
8979
numAnsStr += Integer.toString(num);
9080
}
91-
9281
// Append the current answer str to the ans list
9382
ans.add(numAnsStr);
9483
}
95-
9684
return ans;
9785
}
9886

9987
public List<String> fizzBuzz3(int n) {
10088
// ans list
10189
List<String> ans = new ArrayList<String>();
102-
10390
// Hash map to store all fizzbuzz mappings.
10491
HashMap<Integer, String> fizzBizzDict =
10592
new HashMap<Integer, String>() {
10693
private static final long serialVersionUID = 7966206953841139705L;
94+
10795
{
10896
put(3, "Fizz");
10997
put(5, "Buzz");
11098
}
11199
};
112-
113100
for (int num = 1; num <= n; num++) {
114101
StringBuilder numAnsStr = new StringBuilder();
115-
116102
for (Integer key : fizzBizzDict.keySet()) {
117-
118103
// If the num is divisible by key,
119104
// then add the corresponding string mapping to current numAnsStr
120105
if (num % key == 0) {
121106
numAnsStr.append(fizzBizzDict.get(key));
122107
}
123108
}
124-
125109
if (numAnsStr.toString().equals("")) {
126110
// Not divisible by 3 or 5, add the number
127111
numAnsStr.append(Integer.toString(num));
128112
}
129-
130113
// Append the current answer str to the ans list
131114
ans.add(numAnsStr.toString());
132115
}
133-
134116
return ans;
135117
}
136118
}

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/easy_collection/others/_461.java‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -26,9 +26,10 @@
2626
*/
2727
public class _461 {
2828
public int hammingDistance(int x, int y) {
29-
int xor = x ^ y, count = 0;
30-
for (int i = 0; i < 32; i++) {
31-
count += (xor >> i) & 1;
29+
int curr = x ^ y, count = 0;
30+
while (curr != 0) {
31+
count++;
32+
curr = curr & (curr - 1);
3233
}
3334
return count;
3435
}

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/hard_collection/math/_149.java‎

Lines changed: 6 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -42,10 +42,9 @@
4242
*/
4343
public class _149 {
4444
public int maxPoints(int[][] points) {
45-
if(points.length<=2) return points.length;
46-
int max=0;
47-
int localMax=0;
48-
45+
if (points.length <= 2) return points.length;
46+
int max = 0;
47+
int localMax;
4948
for (int[] point : points) {
5049
HashMap<String, Integer> map = new HashMap<>();
5150
int overlap = 0;
@@ -67,13 +66,11 @@ public int maxPoints(int[][] points) {
6766
localMax += overlap;
6867
max = Math.max(localMax, max);
6968
}
70-
7169
return max;
7270
}
7371

74-
private int gcd(int x, int y){
75-
if(y==0) return x;
76-
77-
return gcd(y,x%y);
72+
private int gcd(int x, int y) {
73+
if (y == 0) return x;
74+
return gcd(y, x % y);
7875
}
7976
}

‎codes/java/leetcodes/src/main/java/com/hit/basmath/interview/top_interview_questions/hard_collection/math/_179.java‎

Lines changed: 8 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -22,14 +22,12 @@
2222
*/
2323
public class _179 {
2424
public String largestNumber(int[] nums) {
25-
if (nums == null || nums.length == 0)
26-
return "";
27-
25+
if (nums == null || nums.length == 0) return "";
2826
// Convert int array to String array, so we can sort later on
29-
String[] s_num = new String[nums.length];
30-
for (int i = 0; i < nums.length; i++)
31-
s_num[i] = String.valueOf(nums[i]);
32-
27+
String[] strs = new String[nums.length];
28+
for (int i = 0; i < nums.length; i++) {
29+
strs[i] = String.valueOf(nums[i]);
30+
}
3331
// Comparator to decide which string should come first in concatenation
3432
Comparator<String> comp = new Comparator<String>() {
3533
@Override
@@ -39,15 +37,11 @@ public int compare(String str1, String str2) {
3937
return s2.compareTo(s1); // reverse order here, so we can do append() later
4038
}
4139
};
42-
43-
Arrays.sort(s_num, comp);
40+
Arrays.sort(strs, comp);
4441
// An extreme edge case by lc, say you have only a bunch of 0 in your int array
45-
if (s_num[0].charAt(0) == '0')
46-
return "0";
47-
42+
if (strs[0].charAt(0) == '0') return "0";
4843
StringBuilder sb = new StringBuilder();
49-
for (String s : s_num)
50-
sb.append(s);
44+
for (String s : strs) sb.append(s);
5145

5246
return sb.toString();
5347
}

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