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LeetCode 算法题 63. Unique Paths II

分类:algorithm| 发布时间:2017-03-17 13:58:00


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.

题意

接着上一题,给出一个二维数组 0 表示这个格子能走,1 表示这个格子不能走,求出所有的路径。

解法

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

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

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