package com.app.main.LeetCode.dynamic;
/**
* 304
*
* medium
*
* https://leetcode.com/problems/range-sum-query-2d-immutable/
*
* Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2).
*
* Range Sum Query 2D
* The above rectangle (with the red border) is defined by (row1, col1) = (2, 1) and (row2, col2) = (4, 3), which contains sum = 8.
*
* Example:
* Given matrix = [
* [3, 0, 1, 4, 2],
* [5, 6, 3, 2, 1],
* [1, 2, 0, 1, 5],
* [4, 1, 0, 1, 7],
* [1, 0, 3, 0, 5]
* ]
*
* sumRegion(2, 1, 4, 3) -> 8
* sumRegion(1, 1, 2, 2) -> 11
* sumRegion(1, 2, 2, 4) -> 12
* Note:
* You may assume that the matrix does not change.
* There are many calls to sumRegion function.
* You may assume that row1 ≤ row2 and col1 ≤ col2.
*
*
* Created with IDEA
* author:Dingsheng Huang
* Date:2020/1/9
* Time:下午3:46
*/
public class NumMatrix {
private int[][] matrix;
private int[][] dp;
public NumMatrix(int[][] matrix) {
if (matrix.length == 0) {
return;
}
this.matrix = matrix;
dp = new int[matrix.length + 1][matrix[0].length + 1];
for (int i = 0; i < matrix.length; i++) {
for (int j = 0; j < matrix[0].length; j++) {
dp[i + 1][j + 1] = dp[i][j + 1] + dp[i + 1][j] + matrix[i][j] - dp[i][j];
}
}
}
public int sumRegion(int row1, int col1, int row2, int col2) {
if (matrix.length == 0) {
return 0;
}
return dp[row2 + 1][col2 + 1] - dp[row1][col2 + 1] - dp[row2 + 1][col1] + dp[row1][col1];
}
/**
* Your NumMatrix object will be instantiated and called as such:
* NumMatrix obj = new NumMatrix(matrix);
* int param_1 = obj.sumRegion(row1,col1,row2,col2);
*/
}
LeetCode--304--medium--Range-sum-query-2d-immutable
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转载自blog.csdn.net/huangdingsheng/article/details/103914929
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