LeetCode: Unique Paths II 解题报告

Unique Paths II

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Question Solution 

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.

SOULUTION 1:

跟LeetCode: Unique Paths 解题报告 相比，只不过是判断一下当前是不是block，如果是block,直接设置D[i][j] 是0就好了 也就是不可达。 同样在3分钟之内Bug free 秒答，哦耶！

public class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        // 1150
        if (obstacleGrid == null || obstacleGrid.length == 0 || obstacleGrid[0].length == 0) {
            return 0;
        }
        
        int rows = obstacleGrid.length;
        int cols = obstacleGrid[0].length;
        
        int[][] D = new int[rows][cols];
        
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                D[i][j] = 0;
                if (obstacleGrid[i][j] == 1) {
                    D[i][j] = 0;
                } else {
                    if (i == 0 && j == 0) {
                        D[i][j] = 1;
                    }
                    
                    if (i != 0) {
                        D[i][j] += D[i - 1][j];
                    }
                    
                    if (j != 0) {
                        D[i][j] += D[i][j - 1];
                    }
                }
            }
        }
        
        return D[rows - 1][cols - 1];
    }
}