LeetCode 动态规划之矩阵区域和详情

m == mat.length
n == mat[i].length
1 <= m, n, k <= 100
1 <= mat[i][j] <= 100

dp[i+1][j+1] = dp[i][j+1]+dp[i+1][j]+arr[i][j]-dp[i][j];

class Solution {
    public int[][] matrixBlockSum(int[][] mat, int k) {
        int m = mat.length,n = mat[0].length;
        int[][] dp = get_dp(mat,m,n);
        return get_res(dp,m,n,k);
    }
    //获取dp数组
    public int[][] get_dp(int[][] arr,int m,int n){
        int[][] dp = new int[m+1][n+1];
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                dp[i+1][j+1] = dp[i][j+1]+dp[i+1][j]+arr[i][j]-dp[i][j];
        return dp;
    }
    //获取结果
    public int[][] get_res(int[][] dp,int m,int n,int k){
        int[][] res = new int[m][n];
        int x1,y1,x2,y2;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                x1 = Math.max(0,i-k);y1 = Math.max(0,j-k);
                x2 = Math.min(m,i+k+1);y2 = Math.min(n,j+k+1);
                res[i][j] = dp[x2][y2]-dp[x1][y2]-dp[x2][y1]+dp[x1][y1];
            }
        }
        return res;
    }
}