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304.java
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304.java
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__________________________________________________________________________________________________
sample 54 ms submission
class NumMatrix {
long[][] sums;
public NumMatrix(int[][] matrix) {
if (matrix.length == 0 || matrix[0].length == 0) {
return;
}
sums = new long[matrix.length + 1][matrix[0].length + 1];
for (int i = 0; i < matrix.length; i++) {
for (int j = 0; j < matrix[0].length; j++) {
sums[i + 1][j + 1] = (long) matrix[i][j] + sums[i][j + 1] + sums[i + 1][j] - sums[i][j];
}
}
}
public int sumRegion(int row1, int col1, int row2, int col2) {
// if (sums == null) {
// return 0;
// }
return (int) (sums[row2 + 1][col2 + 1] - sums[row1][col2 + 1] - sums[row2 + 1][col1] + sums[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);
*/
__________________________________________________________________________________________________
sample 42368 kb submission
class NumMatrix {
private int[][] dp;
public NumMatrix(int[][] matrix) {
int m = matrix.length;
if(m == 0){
return;
}
int n = matrix[0].length;
dp = new int[m+1][n+1];
for(int i = 1; i <= m; i++){
for(int j = 1; j <= n; 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) {
int iMin = Math.min(row1, row2);
int iMax = Math.max(row1, row2);
int jMin = Math.min(col1, col2);
int jMax = Math.max(col1, col2);
return dp[iMax + 1][jMax + 1] - dp[iMax + 1][jMin] - dp[iMin][jMax + 1] + dp[iMin][jMin];
}
}
/**
* Your NumMatrix object will be instantiated and called as such:
* NumMatrix obj = new NumMatrix(matrix);
* int param_1 = obj.sumRegion(row1,col1,row2,col2);
*/
__________________________________________________________________________________________________