https://leetcode.com/problems/partition-equal-subset-sum/description/

class Solution {public:    bool canPartition(vector
     
      & nums) {        int s = 0;        for (auto i : nums) s+= i;        if (s == 0 || s % 2 != 0)     return false;                // sort nums in desc order, and hopefully we will find the result more quickly.        sort(nums.begin(), nums.end(), [](int a, int b) {
   return a > b;});        return helper(nums, s/2, s/2, 0);    }    // nums[start] will be put in set1/remain1, or set2/remain2    bool helper(vector
      
       & nums, int remain1, int remain2, int start) {        // we found a solution        if (remain1 == nums[start] || remain2 == nums[start])   return true;        // try to put in set1        if (remain1 > nums[start] && helper(nums, remain1-nums[start], remain2, start+1))            return true;        // try to put in set2        if (remain2 > nums[start] && helper(nums, remain1, remain2-nums[start], start+1))            return true;        // otherwise, we fail        return false;    }};