Minimum Path Sum

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.

Note: You can only move either down or right at any point in time.

解题思路：

和前面两个题的思路一样！

public int minPathSum(int[][] grid) {       if(grid == null) return 0;              int xlen = grid.length;       int ylen = grid[0].length;              int[][] arr = new int[xlen][ylen];              arr[xlen-1][ylen-1] = grid[xlen-1][ylen-1];       for(int i = xlen-2;i >= 0; i --){           arr[i][ylen-1] = grid[i][ylen-1]+arr[i+1][ylen-1];       }               for(int j = ylen-2; j >= 0; j --){           arr[xlen-1][j] = grid[xlen-1][j]+arr[xlen-1][j+1];       }              for(int i = xlen-2; i >= 0; i --){           for(int j = ylen-2; j >= 0; j--){               int min = arr[i+1][j]<=arr[i][j+1]?arr[i+1][j]:arr[i][j+1];               arr[i][j]=grid[i][j]+min;           }       }       return arr[0][0];    }