leetcode 698. Partition to K Equal Sum Subsets

698. Partition to K Equal Sum Subsets

Given an array of integers nums and a positive integer k, find whether it's possible to divide this array into k non-empty subsets whose sums are all equal.

Example 1:

Input: nums = [4, 3, 2, 3, 5, 2, 1], k = 4Output: TrueExplanation: It's possible to divide it into 4 subsets (5), (1, 4), (2,3), (2,3) with equal sums.

Note:

1 <= k <= len(nums) <= 16.

0 < nums[i] < 10000.

class Solution {public:    bool canPartitionKSubsets(vector<int>& nums, int k)     {        //先要知道sum是多少        sum = 0;        for (auto it : nums)            sum += it;        if (sum % k != 0) return false;        sum = sum / k;        sort(nums.begin(), nums.end(), greater<int>());        for (int i = 0; i < k; i++)            group.push_back(0);        return helper(nums, 0, group, sum);    }        bool helper(vector<int>& nums,                 int i,   //当前需要安排第i个                vector<int> group,                int all) //每一组的和    {        if (i == nums.size()) return true;        for (int j = 0; j < group.size(); j++)        {            if (group[j] + nums[i] <= all) //可以往里面放            {                group[j] += nums[i];                 if (helper(nums, i + 1, group, all)) return true;                group[j] -= nums[i];            }        }        return false;    }    private:    int sum;    vector<int> group;};