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Commit 9430ae6

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add: Target Sum
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‎README.md‎

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@@ -56,6 +56,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
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|404|[Sum of Left Leaves](https://leetcode.com/problems/sum-of-left-leaves/) | [JavaScript](./src/sum-of-left-leaves/res.js)|Easy|
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|416|[Partition Equal Subset Sum](https://leetcode.com/problems/partition-equal-subset-sum/) | [JavaScript](./src/partition-equal-subset-sum/res.js)|Medium|
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|434|[Number of Segments in a String](https://leetcode.com/problems/number-of-segments-in-a-string/) | [JavaScript](./src/number-of-segments-in-a-string/res.js)|Easy|
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|494|[Target Sum](https://leetcode.com/problems/target-sum/) | [JavaScript](./src/target-sum/res.js)|Medium|
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|516|[Longest Palindromic Subsequence](https://leetcode.com/problems/longest-palindromic-subsequence/) | [JavaScript](./src/longest-palindromic-subsequence/res.js)|Medium|
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|523|[Continuous Subarray Sum](https://leetcode.com/problems/continuous-subarray-sum/) | [JavaScript](./src/continuous-subarray-sum/res.js)|Medium|
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||[]() | [](./src//res.js)||

‎src/target-sum/res.js‎

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/**
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* res.js
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* @authors Joe Jiang (hijiangtao@gmail.com)
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* @date 2017年04月12日 21:55:49
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*
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* You are given a list of non-negative integers, a1, a2, ..., an, and a target, S. Now you have 2 symbols + and -. For each integer, you should choose one from + and - as its new symbol.
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*
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* Find out how many ways to assign symbols to make sum of integers equal to target S.
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*
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* Solution idea: https://discuss.leetcode.com/topic/76243/java-15-ms-c-3-ms-o-ns-iterative-dp-solution-using-subset-sum-with-explanation
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*
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* @param {number[]} nums
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* @param {number} S
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* @return {number}
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*/
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let findTargetSumWays = function(nums, S) {
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let len = nums.length,
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res = 0;
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for (let i=0; i<len; i++) {
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res += nums[i];
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}
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if ((res < S && res > -S) || (res+S) & 1) return 0;
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return count(nums, len, (res+S)>>>1);
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};
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/**
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* 计算子集存在满足等于 S 的情况数
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* @param {[type]} nums 数组
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* @param {[type]} len 数组长度
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* @param {[type]} S 计算总和
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* @return {[type]} [description]
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*/
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let count = function(nums, len, S) {
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let arr = new Array(S+1);
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arr[0] = 1;
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for (let i=1; i<=S; i++) {
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arr[i] = 0;
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}
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// 遍历 nums 更新 arr 数组
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for (let i=0; i<len; i++) {
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for (let j=S; j>=nums[i]; j--) {
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arr[j] += arr[j-nums[i]];
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}
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}
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return arr[S];
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}

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