[Leetcode] Unique Paths II

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.

 

将obstacle标记为-1，其余基本跟上一题一样。

 

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