【LeetCode】63. Unique Paths II

题目描述

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.

解题思路

动态规划。
思路与【LeetCode】62. Unique Paths 基本相同。
只是此处需要加多一个对于障碍物obstacle的判断，如果所在的地方是障碍物，那么应该将它的状态设置为0，因为没有任何路线可以到达它。
注意开始处和结束处不可以是障碍物。

AC代码

class Solution {public:    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {        int ans = 0;        int m = obstacleGrid.size(); if (m == 0) return ans;        int n = obstacleGrid[0].size(); if (n == 0) return ans;        if (obstacleGrid[0][0] || obstacleGrid[m - 1][n - 1])            return ans;        vector<vector<int>> dp;        for (int i = 0; i <= m; ++i) {            vector<int> temp(n + 1, 0);            dp.push_back(temp);        }        for (int i = 1; i <= m; ++i) {            for (int j = 1; j <= n; ++j) {                if (i == 1 && j == 1)                    dp[i][j] = 1;                else if (obstacleGrid[i - 1][j - 1])                    dp[i][j] = 0;                else                     dp[i][j] = dp[i][j - 1] + dp[i - 1][j];            }        }        return dp[m][n];    }};