416. Partition Equal Subset Sum

sort之后 看有没有可以等于sum/2的

 

class Solution {
    public boolean canPartition(int[] nums) {
        if(nums.length == 0) return false;
        int sum = 0;
        for(int i = 0; i < nums.length; i++){
            sum += nums[i];
        }
        Arrays.sort(nums);
        if(nums[nums.length - 1] > sum/2) return false;
        if(sum % 2 != 0) return false;
        return dfs(nums, sum/2, nums.length-1);
        
    }
    
    public boolean dfs(int[] nums, int target, int start){
        if(target == 0) return true;
        if(target < 0) return false;
        for(int i = start; i >= 0; i--){
            if(dfs(nums, target - nums[i], i-1)){  //这便是i-1！！
                return true;
            }
        }
        return false;
    }
    
}