学步园

题目：

Follow up for "Unique Paths":

Now consider if some obstacles are added to the grids. How many unique paths would there be?

An obstacle and empty space is marked as 1 and 0 respectively
in the grid.

For example,

There is one obstacle in the middle of a 3x3 grid as illustrated below.

[
  [0,0,0],
  [0,1,0],
  [0,0,0]
]

The total number of unique paths is 2.

Note: m and n will be at most 100.

解题：

类似于Unique Paths，简单DP，状态转移方程：f[i][j] = f[i - 1][j] + f[i][j]

只是注意0，1问题，1的话f[i][j] = 0

代码：

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {
        int row = obstacleGrid.size();
        if(!row) return 0;
        int col = obstacleGrid[0].size();
        vector<vector<int> > f(row, vector<int>(col, 0));
        f[0][0] = !obstacleGrid[0][0];
        for(int i = 0; i < row; i ++) {
            for(int j = 0; j < col; j ++) {
                if(obstacleGrid[i][j]) {
                    f[i][j] = 0;
                    continue;
                }
                if(i) f[i][j] += f[i - 1][j];
                if(j) f[i][j] += f[i][j - 1];
            }
        }
        return f[row - 1][col - 1];
    }
};