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## LeetCode 算法题 63. Unique Paths II

### 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.

### 解法

``````class Solution {
public:
int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
int m = obstacleGrid.size(), n = obstacleGrid.size();
vector<vector<int>> board(m, vector<int>(n, 0));

// init first col
for (int i = 0; i < m; ++i) {
if (obstacleGrid[i]) break;
board[i] = 1;
}

// init first row
for (int i = 0; i < n; ++i) {
if (obstacleGrid[i]) break;
board[i] = 1;
}

for (int i = 1; i < m; ++i) {
for (int j = 1; j < n; ++j) {
if (obstacleGrid[i][j]) {
board[i][j] = 0;
} else {
board[i][j] = board[i - 1][j] + board[i][j - 1];
}
}
}

return board[m - 1][n - 1];
}
};
``````