【第41天】等和子集

1.Partition Equal Subset Sum

这个是01背包问题。一定要复习啊。

class Solution {
    public boolean canPartition(int[] nums) {
        int sum = 0;
        for(int i = 0; i < nums.length; ++i){
            sum += nums[i];
        }

        if (sum % 2 == 1) return false;

        int[] dp = new int[sum/2 +1];
        int target = sum/2;

        for(int i = 0; i < nums.length; ++i){
            for(int j = target; j >= nums[i]; --j){
                dp[j] = Math.max(dp[j-nums[i]] + nums[i], dp[j]);
            }
        }

        return dp[target] == target;

    }
}

2.Last Stone Weight II

class Solution {
    public int lastStoneWeightII(int[] stones) {
        int sum = 0;

        for(int stone: stones){
            sum += stone;
        }

        int target = sum/2;
        int[] dp = new int[target+1];

        for(int i = 0; i < stones.length; ++i){
            for(int j = target; j >= stones[i]; --j){
                dp[j] = Math.max(dp[j], dp[j-stones[i]] + stones[i]);
            }
        }

        return sum - dp[target] - dp[target];
    }
}