leetcode 416. 分割等和子集(java)

刚听完y总的课 学习一下0-1背包

优化好难理解 呜呜呜

练习一下

class Solution {
    public boolean canPartition(int[] nums) {
        int n = nums.length;
        if(n < 2) return false;
        int sum = 0;
        int max = 0;
        for(int i = 0; i < n; i ++){
            sum += nums[i];
            max = Math.max(max, nums[i]);
        }
        if(sum % 2 != 0) return false;
        int half = sum / 2;
        if(max > half) return false;

        boolean[][] dp = new boolean[n][half + 1];
        dp[0][nums[0]] = true;
        for(int i = 1; i < n; i ++){
            for(int j = 1; j <= half; j ++){
                if(j >= nums[i]){
                    dp[i][j] = dp[i - 1][j] || dp[i - 1][j - nums[i]];
                }else{
                    dp[i][j] = dp[i - 1][j]; 
                }
            }
        }
        return dp[n - 1][half];
    }
}

​​​​​​​

class Solution {
    public boolean canPartition(int[] nums) {
        int n = nums.length;
        if(n < 2) return false;
        int sum = 0;
        int max = 0;
        for(int i = 0; i < n; i ++){
            sum += nums[i];
            max = Math.max(max, nums[i]);
        }
        if(sum % 2 != 0) return false;
        int half = sum / 2;
        if(max > half) return false;

        boolean[] dp = new boolean[half + 1];
        dp[0] = true;
        for(int i = 1; i < n; i ++){
            for(int j = half; nums[i]<= j; j --){
                if (dp[half]) {
                    return true;
                }
                dp[j] = dp[j] || dp[j - nums[i]]; 
            }
        }
        return dp[half];
    }
}