LeetCode - Unique Paths II
Problem description
A robot is located at the top-left corner of a m x n grid (marked ‘Start’ in the diagram below).
The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked ‘Finish’ in the diagram below).
How many possible unique paths are there?
An obstacle and empty space is marked as 1 and 0 respectively in the grid.
Note: m and n will be at most 100.
Example 1:
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Input:
[
[0,0,0],
[0,1,0],
[0,0,0]
]
Output: 2
Explanation:
There is one obstacle in the middle of the 3x3 grid above.
There are two ways to reach the bottom-right corner:
1. Right -> Right -> Down -> Down
2. Down -> Down -> Right -> Right
Analysis
use DP as the unique paths.
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public int uniquePathsWithObstacles(int[][] obstacleGrid) {
int m = obstacleGrid.length;
int n = obstacleGrid[0].length;
if (obstacleGrid[0][0] == 1 || obstacleGrid[m-1][n-1] == 1){
return 0;
}
int[][] dp = new int[m][n];
dp[0][0] = 1;
for (int i = 1; i < m; i++){
if (obstacleGrid[i - 1][0] != 1)
dp[i][0] = 1;
else{
break;
}
}
for (int i = 1; i < n; i++){
if (obstacleGrid[0][i - 1] != 1)
dp[0][i] = 1;
else{
break;
}
}
for (int i = 1; i < m; i++){
for (int j = 1; j < n; j++){
if (obstacleGrid[i-1][j] == 0){
dp[i][j] += dp[i-1][j];
}
if (obstacleGrid[i][j-1] == 0){
dp[i][j] += dp[i][j-1];
}
}
}
return dp[m-1][n-1];
}