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LeetCode-304-Range-Sum-Query-2D-Immutable.java
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LeetCode-304-Range-Sum-Query-2D-Immutable.java
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class NumMatrix {
int[][] sum;
public NumMatrix(int[][] matrix) {
if (matrix != null && matrix.length > 0 && matrix[0].length > 0) {
sum = new int[matrix.length][matrix[0].length];
sum[0][0] = matrix[0][0];
for (int i = 1; i < matrix.length; i++) {
sum[i][0] = sum[i - 1][0] + matrix[i][0];
}
for (int j = 1; j < matrix[0].length; j++) {
sum[0][j] = sum[0][j - 1] + matrix[0][j];
}
for (int i = 1; i < matrix.length; i++) {
for (int j = 1; j < matrix[0].length; j++) {
sum[i][j] = sum[i - 1][j] + sum[i][j - 1] - sum[i - 1][j - 1] + matrix[i][j];
}
}
}
}
public int sumRegion(int row1, int col1, int row2, int col2) {
if (row1 == 0 && col1 == 0) return sum[row2][col2];
if (row1 == 0) return sum[row2][col2] - sum[row2][col1 - 1];
if (col1 == 0) return sum[row2][col2] - sum[row1 - 1][col2];
return sum[row2][col2] - sum[row1 - 1][col2] - sum[row2][col1 - 1] + sum[row1 - 1][col1 - 1];
}
}
/**
* Your NumMatrix object will be instantiated and called as such:
* NumMatrix obj = new NumMatrix(matrix);
* int param_1 = obj.sumRegion(row1,col1,row2,col2);
*/