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| 1 | +// Source : https://leetcode.com/problems/target-sum/ |
| 2 | +// Author : Han Zichi |
| 3 | +// Date : 2017年01月22日 |
| 4 | + |
| 5 | +/** |
| 6 | + * @param {number[]} nums |
| 7 | + * @param {number} S |
| 8 | + * @return {number} |
| 9 | + */ |
| 10 | +var findTargetSumWays = function(nums, S) { |
| 11 | + let total = 0 |
| 12 | + , len = nums.length; |
| 13 | + |
| 14 | + for (let item of nums) |
| 15 | + total += item; |
| 16 | + |
| 17 | + let target = total - S; |
| 18 | + |
| 19 | + if (target & 1) |
| 20 | + return 0; |
| 21 | + |
| 22 | + target >>= 1; |
| 23 | + |
| 24 | + // select items from nums whose sum is `target` |
| 25 | + nums.sort((a, b) => b - a); // 1000ms |
| 26 | + // nums.sort((a, b) => a - b); // 1400ms |
| 27 | + |
| 28 | + let ans = 0; |
| 29 | + |
| 30 | + let dfs = (index, sum) => { |
| 31 | + if (sum === target) { |
| 32 | + ans++; |
| 33 | + // consider that nums contains 0 |
| 34 | + // return; |
| 35 | + } |
| 36 | + |
| 37 | + if (index === len || sum > target) |
| 38 | + return; |
| 39 | + |
| 40 | + for (let i = index; i < len; i++) |
| 41 | + dfs(i + 1, sum + nums[i]); |
| 42 | + }; |
| 43 | + |
| 44 | + dfs(0, 0); |
| 45 | + |
| 46 | + return ans; |
| 47 | +}; |
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