【LeetCode】Unique Paths II 解题报告
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【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
.
Note: m and n will be at most 100.
【解析】题意:数组 A[m][n] ,从 A[0][0] 到 A[m-1][n-1] 有多少条路径,A[m][n] 中可能存在障碍,即A[i][j] = 1 时。
与 【LeetCode】Unique Paths 解题报告不同的是,数组中多了障碍,其实只要把障碍地方的解变为 0 就好。
【动态规划】
public class Solution { public int uniquePathsWithObstacles(int[][] obstacleGrid) { int rows = obstacleGrid.length; if (rows < 1) return 0; int cols = obstacleGrid[0].length; if (cols < 1) return 0; if (obstacleGrid[0][0] == 1 || obstacleGrid[rows - 1][cols - 1] == 1) return 0; int[] ans = new int[cols]; ans[0] = 1; for (int j = 1; j < cols; j++) { if (obstacleGrid[0][j] == 0) { ans[j] = ans[j - 1]; } else { ans[j] = 0; } } for (int i = 1; i < rows; i++) { if (obstacleGrid[i][0] == 1) { ans[0] = 0; } for (int j = 1; j < cols; j++) { if (obstacleGrid[i][j] == 1) { ans[j] = 0; } else { ans[j] += ans[j - 1]; } } } return ans[cols - 1]; }}
题目比较怪异的地方是有一个测试用例为 [[1]] ,即起点和终点重合,而且是障碍。
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