[leetcode]304. Range Sum Query 2D - Immutable
阿新 • • 發佈:2018-12-17
整體的思路一樣。就是dp這個怎麼求沒想出來
class NumMatrix { private int[][] dp; public NumMatrix(int[][] matrix) { if (matrix.length == 0 || matrix[0].length == 0) return; dp = new int[matrix.length + 1][matrix[0].length + 1]; for (int r = 0; r < matrix.length; r++) { for (int c = 0; c < matrix[0].length; c++) { dp[r + 1][c + 1] = dp[r + 1][c] + dp[r][c + 1] + matrix[r][c] - dp[r][c]; } } } public int sumRegion(int row1, int col1, int row2, int col2) { return dp[row2 + 1][col2 + 1] - dp[row1][col2 + 1] - dp[row2 + 1][col1] + dp[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); */