05 August 2008
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class NumMatrix {
/*
https://leetcode.com/problems/range-sum-query-2d-mutable/discuss/75870/Java-2D-Binary-Indexed-Tree-Solution-clean-and-short-17ms
*/
private int[][] nums;
private int[][] binaryIndexTree;
private int m;
private int n;
public NumMatrix(int[][] matrix) {
m = matrix.length;
if (m == 0) {
return;
}
n = matrix[0].length;
nums = new int[m][n];
binaryIndexTree = new int[m+1][n+1];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
update(i, j, matrix[i][j]);
}
}
}
public void update(int row, int col, int val) {
int vary = val - nums[row][col];
nums[row][col] = val;
for (int i = row + 1; i <= m; i += i & (-i)) {
for (int j = col + 1; j <= n; j += j & (-j)) {
binaryIndexTree[i][j] += vary;
}
}
}
public int sumRegion(int row1, int col1, int row2, int col2) {
return sum(row1, col1) + sum(row2+1, col2+1) - sum(row1, col2 + 1) - sum(row2 + 1, col1);
}
private int sum(int row, int col) {
int sum = 0;
for (int i = row; i > 0; i -= i & (-i)) {
for (int j = col; j > 0; j -= j & (-j)) {
sum += binaryIndexTree[i][j];
}
}
return sum;
}
}
/**
* Your NumMatrix object will be instantiated and called as such:
* NumMatrix obj = new NumMatrix(matrix);
* obj.update(row,col,val);
* int param_2 = obj.sumRegion(row1,col1,row2,col2);
*/