1314. Matrix Block Sum

Given a m * n matrix mat and an integer K, return a matrix answer where each answer[i][j] is the sum of all elements mat[r][c] for i - K <= r <= i + K, j - K <= c <= j + K, and (r, c) is a valid position in the matrix.

Example 1:

Input: mat = [[1,2,3],[4,5,6],[7,8,9]], K = 1
Output: [[12,21,16],[27,45,33],[24,39,28]]

Example 2:

Input: mat = [[1,2,3],[4,5,6],[7,8,9]], K = 2
Output: [[45,45,45],[45,45,45],[45,45,45]]

Constraints:

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

class Solution {
 public int[][] matrixBlockSum(int[][] mat, int K) {
        int m = mat.length, n = mat[0].length;
        int[][] rangeSum = new int[m + 1][n + 1];
        for (int i = 0; i < m; ++i)
            for (int j = 0; j < n; ++j)
                rangeSum[i + 1][j + 1] = rangeSum[i + 1][j] + rangeSum[i][j + 1] - rangeSum[i][j] + mat[i][j];
        int[][] ans = new int[m][n];
        for (int i = 0; i < m; ++i)
            for (int j = 0; j < n; ++j) {
                int r1 = Math.max(0, i - K), c1 = Math.max(0, j - K), r2 = Math.min(m, i + K + 1), c2 = Math.min(n, j + K + 1);
                ans[i][j] = rangeSum[r2][c2] - rangeSum[r2][c1] - rangeSum[r1][c2] + rangeSum[r1][c1];
            }
        return ans;
    }
}

 https://leetcode.com/problems/matrix-block-sum/discuss/477036/JavaPython-3-PrefixRange-sum-w-analysis-similar-to-LC-30478

石头哥真乃人间奇才。

304. range sum query

标签：rangeSum,1314,Matrix,int,Sum,45,sum,Math,mat
来源： https://www.cnblogs.com/wentiliangkaihua/p/12196298.html