64. 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.

Example 1:

[[1,3,1], 

 [1,5,1], 

 [4,2,1]]

Given the above grid map, return 7. Because the path 1→3→1→1→1 minimizes the sum.

 

public int minPathSum(int[][] grid) {

       int m = grid.length;

       int n = grid[0].length;

       for (int i = 0; i < m; i++) {

           for (int j = 0; j < n; j++) {

              if (i == 0 && j != 0)

                 grid[i][j] = grid[i][j] + grid[i][j - 1]; //对于第一行

              else if (i != 0 && j == 0)

                 grid[i][j] = grid[i][j] + grid[i - 1][j]; //对于第一列

              else if (i == 0 && j == 0)

                 grid[i][j] = grid[i][j];

              else

                 grid[i][j] += Math.min(grid[i][j - 1], grid[i - 1][j]); //看此格左和上哪个更小

              

           }

       }

     return grid[m - 1][n - 1];  

    }