LeetCode

Given a non-empty array containing only positive integers, find if the array can be partitioned into two subsets such that the sum of elements in both subsets is equal.

Note:

1. Each of the array element will not exceed 100.
2. The array size will not exceed 200.

Example 1:

Input: [1, 5, 11, 5]Output: trueExplanation: The array can be partitioned as [1, 5, 5] and [11].

Example 2:

Input: [1, 2, 3, 5]Output: falseExplanation: The array cannot be partitioned into equal sum subsets.

问一个数组能不能划分成和相等的两部分。

可以转化为0/1背包做。先求出数组和，若为奇数，则肯定无法划分，若是偶数sum，则相当于求数组中是否存在子集和 = sum / 2

背包还是两年前跟着连飞学的，居然都过去这么久了，叹气。。。

class Solution {public:    bool canPartition(vector<int>& nums) {        int sum = 0;        for (auto x: nums) sum += x;        if (sum & 1) return false;        sum >>= 1;        vector<int> dp(sum+1, 0);        dp[0] = 1;        for (auto x: nums) {            for (int i = sum; i >= x; --i) {                dp[i] += dp[i-x];            }        }        if (dp[sum]) return true;        return false;    }};