LeetCode | Unique Paths II

題目

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.

Note: m and n will be at most 100.

用和Unique Paths中一樣的動態規劃就行了，注意首部和障礙物即可。

代碼

public class UniquePathsII {
	public int uniquePathsWithObstacles(int[][] obstacleGrid) {
		if (obstacleGrid == null || obstacleGrid.length == 0) {
			return 0;
		}
		int M = obstacleGrid.length;
		int N = obstacleGrid[0].length;
		// init
		int[] dp = new int[N];
		dp[0] = 1;
		// dp
		for (int i = 0; i < M; ++i) {
			dp[0] = obstacleGrid[0][0] == 1 ? 0 : dp[0];
			for (int j = 1; j < N; ++j) {
				if (obstacleGrid[i][j] == 1) {
					dp[j] = 0;
				} else {
					dp[j] += dp[j - 1];
				}
			}
		}
		return dp[N - 1];
	}
}