/**
* https://leetcode.com/articles/range-sum-query-2d-immutable/
*/
public class NumMatrix {
private int[][] dp;
public NumMatrix(int[][] matrix) {
if (matrix.length == 0) {
return;
}
int row = matrix.length;
int col = matrix[0].length;
dp = new int[row + 1][col + 1];
for (int i = 1; i <= row; i++) {
for (int j = 1; j <= col; j++) {
dp[i][j] = dp[i - 1][j] + dp[i][j - 1] - dp[i - 1][j - 1] + matrix[i - 1][j - 1];
}
}
}
public int sumRegion(int row1, int col1, int row2, int col2) {
return dp[row2 + 1][col2 + 1] - dp[row2 + 1][col1] - dp[row1][col2 + 1] + dp[row1][col1];
}
}
// Your NumMatrix object will be instantiated and called as such:
// NumMatrix numMatrix = new NumMatrix(matrix);
// numMatrix.sumRegion(0, 1, 2, 3);
// numMatrix.update(1, 1, 10);
// numMatrix.sumRegion(1, 2, 3, 4);