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.

从左上方到右下方，只能向下和向右移动。按行进行处理。

    public int minPathSum(int[][] grid) {
        if (grid == null) {
            return 0;
        }
        int lenI = grid.length;
        if (lenI == 0) {
            return 0;
        }
        int lenJ = grid[0].length;
        if (lenJ == 0) {
            return 0;
        }
        
        for (int i = 0; i < lenI; i++) {
            for (int j = 0; j < lenJ; j++) {
                if (!(i == 0 && j ==0)) {
                    if (i == 0) {
                        grid[i][j] = grid[i][j - 1] + grid[i][j];
                    } else if (j == 0) {
                        grid[i][j] = grid[i - 1][j] + grid[i][j];
                    } else {
                        grid[i][j] = Math.min(grid[i][j - 1] + grid[i][j], grid[i - 1][j] + grid[i][j]);
                    }
                }
            }
        }
        return grid[lenI - 1][lenJ - 1];
    }