LeetCode--689_Maximum_Sum_of_3_NonOverlapping_Subarrays

Posted 2021-02-17 dyloder

原题链接：点击这里

一道很水很水的背包问题？ 大概算不上背包吧QAQ 自己的dp 真的是太差劲啦，以后每天一道LeetCode 备战秋招！

package leetcode;

public class a689_Maximum_Sum_of_3_NonOverlapping_Subarrays {
    
    public static int[] maxSumOfThreeSubarrays(int[] nums, int k) {
        int [] ans = new int [3];
        int [][] dp = new int [3][nums.length+1];
        
        int [] sum = new int [nums.length+1];
        for(int j=1;j<=nums.length;j++) {
            if(j==1) {
                sum[j]=nums[j-1];
            }else {
                sum[j]+=sum[j-1]+nums[j-1];
            }
        }
        int mmx =0;
        for(int j=0;j<3;j++) {
            int max = 0;
            for(int i = k*j+1;i<=nums.length-k+1;i++) {
                if(j==0) {
                    dp[0][i] = sum[i+k-1]-sum[i-1];
                }else {
                    max = Math.max(max, dp[j-1][i-k]);
                    dp[j][i] = max+sum[i+k-1]-sum[i-1];
                    mmx = Math.max(mmx, dp[j][i]);
                }
            }
        }
        
        for(int j=2;j>=0;j--) {
            for(int i=1;i<=nums.length-k+1;i++) {
                if(dp[j][i]==mmx) {
                    ans[j]=i-1;
                    mmx -= sum[i+k-1]-sum[i-1];
                    break;
                }
            }
        }
        return ans;
    }
    
    public static void main(String[] args) {
        
        int [] nums = {1,2,1,2,6,7,5,1};
        int k = 2;
        maxSumOfThreeSubarrays(nums,k);
    }

}

Runtime: 4 ms, faster than 82.08% of Java online submissions for Maximum Sum of 3 Non-Overlapping Subarrays.

Memory Usage: 42.6 MB, less than 34.91% of Java online submissions forMaximum Sum of 3 Non-Overlapping Subarrays.