leetcode 63

python

Author: kyle8998

README.md

@@ -55,6 +55,7 @@ Personal Practice Set - Doing One a Day (sometimes) in a Variety of Languages (M
 | 56 | Medium     | [Merge Intervals](leetcode/56-Medium-Merge-Intervals/problem.md)                             | [Python](leetcode/56-Medium-Merge-Intervals/answer.py)            |
 | 58 | Easy       | [Length of Last Word](leetcode/58-Easy-Length-Of-Last-Word/problem.md)                       | [Python](leetcode/58-Easy-Length-Of-Last-Word/answer.py)          |
 | 62 | Medium     | [Unique Paths](leetcode/62-Medium-Unique-Paths/problem.md)                                   | [Python](leetcode/62-Medium-Unique-Paths/answer.py)               |
+| 63 | Medium     | [Unique Paths II](leetcode/63-Medium-Unique-Paths-II/problem.md)                             | [Python](leetcode/63-Medium-Unique-Paths-II/answer.py)            |
 | 64 | Medium     | [Minimum Path Sum](leetcode/64-Medium-Minimum-Path-Sum/problem.md)                           | [Python](leetcode/64-Medium-Minimum-Path-Sum/answer.py)           |
 | 66 | Easy       | [Plus One](leetcode/66-Easy-Plus-One/problem.md)                                             | [Python](leetcode/66-Easy-Plus-One/answer.py)                     |
 | 67 | Easy       | [Add Binary](leetcode/67-Easy-Add-Binary/problem.md)                                         | [Python](leetcode/67-Easy-Add-Binary/answer.py)                   |

leetcode/63-Medium-Unique-Paths-II/answer.py

@@ -0,0 +1,38 @@
+#!/usr/bin/python3
+
+#------------------------------------------------------------------------------
+
+class Solution(object):
+    def uniquePathsWithObstacles(self, grid):
+        """
+        :type obstacleGrid: List[List[int]]
+        :rtype: int
+        """
+        if not grid or not grid[0] or grid[0][0] == 1:
+            return 0
+        # **NOTE** Cannot use multiplication because it copies references
+        # Must use list comprehension for this to create cache
+        # cache = [[0]*len(grid[0])]*len(grid)
+        cache = [[0]*len(grid[0]) for _ in range(len(grid))]
+        cache[0][0] = 1
+        
+        # Set side paths
+        for row in range(1, len(grid)):
+            if grid[row][0] == 1:
+                break
+            cache[row][0] = 1
+        for col in range(1, len(grid[0])):
+            if grid[0][col] == 1:
+                break
+            cache[0][col] = 1
+        
+        # Set rest of cache
+        for row in range(1, len(grid)):
+            for col in range(1, len(grid[0])):
+                if grid[row][col] == 0:
+                    cache[row][col] = cache[row-1][col] + cache[row][col-1]
+        
+        return cache[-1][-1]
+        
+#------------------------------------------------------------------------------
+#Testing

leetcode/63-Medium-Unique-Paths-II/problem.md

@@ -0,0 +1,33 @@
+# Problem 63: Unique Paths II
+
+#### Difficulty: Medium
+
+#### Problem
+
+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).
+
+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.
+
+#### Example
+
+<pre>
+
+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
+
+</pre>
+