When using the sum of the [0,0] to [i,j], the ** TLE** will occur. So I decrease the time of preprocessing by summarizing the column num.

```
public class NumMatrix {
int[][] sums;
public NumMatrix(int[][] matrix) {
if (matrix.length == 0) {
return;
}
this.sums = new int[matrix.length + 1][matrix[0].length];
for (int i = 0; i < matrix.length; i++) {
for (int j = 0; j < matrix[0].length; j++) {
sums[i + 1][j] = sums[i][j] + matrix[i][j];
}
}
}
public int sumRegion(int row1, int col1, int row2, int col2) {
int sum = 0;
for(int i = col1; i <= col2; i++) {
sum += sums[row2 + 1][i] - sums[row1][i];
}
return sum;
}
}
```

but with this way, time is 146ms.

How to do to get the time less?