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RangeSumQuery2DImmutable.java
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RangeSumQuery2DImmutable.java
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package Leetcode;
/**
* @author kalpak
*
* 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).
*
* Implement the NumMatrix class:
*
* NumMatrix(int[][] matrix) initializes the object with the integer matrix matrix.
* int sumRegion(int row1, int col1, int row2, int col2)
* returns the sum of the elements of the matrix array inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2).
*/
public class RangeSumQuery2DImmutable {
private int[][] dp;
public RangeSumQuery2DImmutable(int[][] matrix) {
if(matrix.length == 0 || matrix[0].length == 0)
return;
dp = new int[matrix.length + 1][matrix[0].length + 1];
for(int r = 0; r < matrix.length; r++) {
for(int c = 0; c < matrix[0].length; c++)
dp[r + 1][c + 1] = dp[r + 1][c] + dp[r][c + 1] + matrix[r][c] - dp[r][c];
}
}
public int sumRegion(int row1, int col1, int row2, int col2) {
return dp[row2 + 1][col2 + 1] - dp[row1][col2 + 1] - dp[row2 + 1][col1] + dp[row1][col1];
}
}