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Commit 9658b0b

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feat: solve No.645,907
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‎601-700/645. Set Mismatch.md‎

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# 645. Set Mismatch
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- Difficulty: Easy.
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- Related Topics: Array, Hash Table, Bit Manipulation, Sorting.
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- Similar Questions: Find the Duplicate Number.
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## Problem
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You have a set of integers `s`, which originally contains all the numbers from `1` to `n`. Unfortunately, due to some error, one of the numbers in `s` got duplicated to another number in the set, which results in **repetition of one** number and **loss of another** number.
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You are given an integer array `nums` representing the data status of this set after the error.
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Find the number that occurs twice and the number that is missing and return **them in the form of an array**.
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Example 1:
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```
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Input: nums = [1,2,2,4]
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Output: [2,3]
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```Example 2:
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```
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Input: nums = [1,1]
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Output: [1,2]
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```
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**Constraints:**
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- `2 <= nums.length <= 104`
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- `1 <= nums[i] <= 104`
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## Solution
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```javascript
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/**
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* @param {number[]} nums
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* @return {number[]}
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*/
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var findErrorNums = function(nums) {
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var missing = 0;
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var duplicated = 0;
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for (var i = 0; i < nums.length; i++) {
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if (nums[Math.abs(nums[i]) - 1] < 0) {
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duplicated = Math.abs(nums[i]);
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} else {
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nums[Math.abs(nums[i]) - 1] *= -1;
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}
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}
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for (var i = 0; i < nums.length; i++) {
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if (nums[i] > 0) {
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missing = i + 1;
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}
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}
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return [duplicated, missing];
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};
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```
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**Explain:**
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nope.
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**Complexity:**
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* Time complexity : O(n).
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* Space complexity : O(1).
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# 907. Sum of Subarray Minimums
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- Difficulty: Medium.
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- Related Topics: Array, Dynamic Programming, Stack, Monotonic Stack.
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- Similar Questions: Sum of Subarray Ranges, Sum of Total Strength of Wizards.
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## Problem
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Given an array of integers arr, find the sum of `min(b)`, where `b` ranges over every (contiguous) subarray of `arr`. Since the answer may be large, return the answer **modulo** `109 + 7`.
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Example 1:
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```
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Input: arr = [3,1,2,4]
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Output: 17
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Explanation:
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Subarrays are [3], [1], [2], [4], [3,1], [1,2], [2,4], [3,1,2], [1,2,4], [3,1,2,4].
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Minimums are 3, 1, 2, 4, 1, 1, 2, 1, 1, 1.
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Sum is 17.
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```
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Example 2:
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```
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Input: arr = [11,81,94,43,3]
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Output: 444
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```
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**Constraints:**
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- `1 <= arr.length <= 3 * 104`
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- `1 <= arr[i] <= 3 * 104`
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## Solution
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```javascript
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/**
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* @param {number[]} arr
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* @return {number}
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*/
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var sumSubarrayMins = function(arr) {
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var stack = [];
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var rightBiggerNums = Array(arr.length).fill(1);
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for (var i = 0; i <= arr.length; i++) {
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while (stack.length && (i === arr.length || arr[i] < arr[stack[stack.length - 1]])) {
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var index = stack.pop();
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rightBiggerNums[index] = i - index;
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}
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stack.push(i);
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}
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stack = [];
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var leftBiggerNums = Array(arr.length).fill(1);
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for (var i = arr.length - 1; i >= -1; i--) {
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while (stack.length && (i === -1 || arr[i] <= arr[stack[stack.length - 1]])) {
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var index = stack.pop();
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leftBiggerNums[index] = index - i;
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}
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stack.push(i);
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}
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var sum = 0;
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var mod = Math.pow(10, 9) + 7;
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for (var i = 0; i < arr.length; i++) {
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sum += rightBiggerNums[i] * leftBiggerNums[i] * arr[i];
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sum %= mod;
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}
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return sum;
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};
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```
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**Explain:**
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Monotonic stack, be careful about duplicate nums.
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**Complexity:**
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* Time complexity : O(n).
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* Space complexity : O(n).

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