"Leetcode" Range Sum Query 2d-immutable

Title Link: https://leetcode.com/problems/range-sum-query-2d-immutable/
Topic:

Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by it upper left corner (Row1, col1) and lower right corner (Row2, col2).

The above rectangle (with the red border) are defined by (row1, col1) = (2, 1) and (Row2, col2) = (4, 3), which contains sum = 8.

Example:

Given matrix = [  [3, 0, 1, 4, 2],  [5, 6, 3, 2, 1],  [1, 2, 0, 1, 5],  [4, 1, 0, 1, 7],  [1, 0, 3, 0, 5]]s Umregion (2, 1, 4, 3), 8sumRegion (1, 1, 2, 2), 11sumRegion (1, 2, 2, 4), 12

Note:

1. Assume that the matrix does not a change.
2. There is many calls to Sumregion function.
3. Assume that Row1≤row2 and col1≤col2.

Ideas:

Simple...

Algorithm:

int s[][]; Public Nummatrix (int[][] matrix) {if (matrix.length! = 0) {s = new INT[MATRIX.LENGTH][MATRIX[0].L              Ength];              S[0][0] = matrix[0][0];              for (int i = 1; i < matrix.length; i++) {s[i][0] = S[i-1][0] + matrix[i][0];              } for (int j = 1; j < Matrix[0].length; J + +) {S[0][j] = S[0][j-1] + matrix[0][j]; } for (int i = 1; i < matrix.length; i++) {for (int j = 1; J < Matrix[0].le Ngth;                  J + +) {S[i][j] = S[i-1][j] + s[i][j-1]-s[i-1][j-1] + matrix[i][j];  }}}} public int sumregion (int row1, int col1, int row2, int col2) {int s2 =          0, s3 = 0, s4 = 0;          if (col1-1 >= 0) s2 = s[row2][col1-1];          if (row1-1 >= 0) s3 = S[row1-1][col2]; if (row1-1 >= 0 && col1-1 >= 0) s4 = s[row1-1][col1-1];      return S[row2][col2]-s2-s3 + S4;   }

"Leetcode" Range Sum Query 2d-immutable