698. Partition to K Equal Sum Subsets

Given an integer array nums and an integer k, return true if it is 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 = 4
Output: true
Explanation: It's possible to divide it into 4 subsets (5), (1, 4), (2,3), (2,3) with equal sums.

Example 2:

Input: nums = [1,2,3,4], k = 3
Output: false

Constraints:

• 1 <= k <= nums.length <= 16
• 1 <= nums[i] <= 104
• The frequency of each element is in the range [1, 4].

class Solution {
    public boolean canPartitionKSubsets(int[] nums, int k) {
        if(nums.length < k) return false;
        int sum = 0;
        for(int i : nums) sum += i;
        if(sum % k != 0) return false;
        boolean[] visited = new boolean[nums.length];
        return dfs(visited, nums, 0, 0, sum / k, k);
    }
    
    public boolean dfs(boolean[] visited, int[] nums, int start, int cur, int target, int k) {
        if(k == 0) return true;
        
        if(cur == target) return dfs(visited, nums, 0, 0, target, k - 1);
        for(int i = start; i < nums.length; i++) {
            if(visited[i] || cur + nums[i] > target) continue;
            visited[i] = true;
            if(dfs(visited, nums, i + 1, cur + nums[i], target, k)) return true;
            visited[i] = false;
        }
        return false;
    }
}