Unique Paths II

注意一个容易犯的错误：判断obstacleGrid是否为1时，else那部分不能少。因为如果不加，就会默认把那些值设置为0。

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

 初始化第一行第一列

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
        int length = obstacleGrid.size();
        if(length <= 0)
            return 0;
        int width = obstacleGrid[0].size();
        vector<vector<int>> result(length,vector<int>(width));
        if(obstacleGrid[0][0] == 1)
            result[0][0] = 0;
        else
            result[0][0] = 1;
        for(int i = 1;i < length;i++){
            if(obstacleGrid[i][0] == 1 || result[i-1][0] == 0)
                result[i][0] = 0;
            else
                result[i][0] = 1;
        }
        for(int j = 1;j < width;j++){
            if(obstacleGrid[0][j] == 1 || result[0][j-1] == 0)
                result[0][j] = 0;
            else
                result[0][j] = 1;
        }
        for(int i = 1;i < length;i++){
            for(int j = 1;j < width;j++){
                if(obstacleGrid[i][j] == 1)
                    result[i][j] = 0;
                //else if(result[i-1][j] == 0)      这些不注释掉也能跑出正确结果
                    //result[i][j] = result[i][j-1];
                //else if(result[i][j-1] == 0)
                    //result[i][j] = result[i-1][j];
                else
                    result[i][j] = result[i][j-1] + result[i-1][j];
            }
        }
        return result[length-1][width-1];
    }
};