62_Unique_Paths

63_Unique_Paths_II
70_Climbing_Stairs

Author: qiyuangong

README.md

@@ -24,8 +24,11 @@
 | 24 | [Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/24_Swap_Nodes_in_Pairs.py) | Add a dummy and store the prev |
 | 28 | [Implement strStr()](https://leetcode.com/problems/implement-strstr/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/28_Implement_strStr().py) | 1. O(nm) comparison <br>2. KMP |
 | 54 | [Spiral Matrix](https://leetcode.com/problems/spiral-matrix/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/54_Spiral_Matrix.py) | O(nm) 1. Turn in the corner and loop<br>2. (0, 1) -> (1, 0) -> (0, -1) -> (-1, 0) |
+| 62 | [Unique Paths](https://leetcode.com/problems/unique-paths/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/62_Unique_Paths.py) | 1. Bottom-up DP, dp[i][j] = dmap[i-1][j] + dmap[i][j-1], O(mn) and O(mn)<br>2. Combination (m+n-2, m-1) |
+| 63 | [Unique Paths II](https://leetcode.com/problems/unique-paths-ii/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/63_Unique_Paths_II.py) | Bottom-up DP, dp[i][j] = dmap[i-1][j] + dmap[i][j-1] (if block, then 0), O(mn) and O(mn) |
 | 65 | [Valid Number](https://leetcode.com/problems/valid-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/65_Valid_Number.py) | 1. strip leading and tailing space, then check float using exception, check e using split <br>2. check is number split by . or e, note that number after e may be negative |
 | 66 | [Plus One](https://leetcode.com/problems/plus-one/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/66_Plus_One.py) | Check if current digit == 9. |
+| 70 | [Climbing Stairs](https://leetcode.com/problems/climbing-stairs/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/70_Climbing_Stairs.py) | Bottom-up DP, dp[i] = dp[i - 2] + dp[i- 1] <br>1. O(n) and O(n)<br>2. Only two variables are needed, O(n) and O(1) |
 | 72 | [Edit Distance](https://leetcode.com/problems/edit-distance/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/72_Edit_Distance.py) | [Background](https://en.wikipedia.org/wiki/Edit_distance)<br> 1. DP O(n^2) space<br>2. DP O(n) space |
 | 98 | [Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/98_Validate_Binary_Search_Tree.py) | 1. Stack O(n) and O(n)<br>2. Recursion O(n) and O(n) |
 | 104 | [Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/104_Maximum_Depth_of_Binary_Tree.py)| Recursion max(left, right) + 1 |

python/62_Unique_Paths.py

@@ -5,10 +5,7 @@ def uniquePaths(self, m, n):
         :type n: int
         :rtype: int
         """
-        dmap = []
-        for i in range(m):
-            temp = [0] * n
-            dmap.append(temp)
+        dmap = [[0] * n for _ in range(m)]
         for i in range(m):
             dmap[i][0] = 1
         for j in range(n):

python/63_Unique_Paths_II.py

@@ -1,32 +1,43 @@
 class Solution(object):
+    # def uniquePathsWithObstacles(self, obstacleGrid):
+    #     """
+    #     :type obstacleGrid: List[List[int]]
+    #     :rtype: int
+    #     """
+    #     m, n = len(obstacleGrid), len(obstacleGrid[0])
+    #     dmap = [[0] * n for _ in range(m)]
+    #     for i in range(m):
+    #         if obstacleGrid[i][0] != 1:
+    #             dmap[i][0] = 1
+    #         else:
+    #             break
+    #     for j in range(n):
+    #         if obstacleGrid[0][j] != 1:
+    #             dmap[0][j] = 1
+    #         else:
+    #             break
+    #     for i in range(1, m):
+    #         for j in range(1, n):
+    #             if obstacleGrid[i][j] == 1:
+    #                 continue
+    #             l = u = 0
+    #             if i - 1 >= 0:
+    #                 u = dmap[i - 1][j]
+    #             if j - 1 >= 0:
+    #                 l = dmap[i][j - 1]
+    #             dmap[i][j] = l + u
+    #     return dmap[m - 1][n - 1]
+
     def uniquePathsWithObstacles(self, obstacleGrid):
-        """
-        :type obstacleGrid: List[List[int]]
-        :rtype: int
-        """
         m, n = len(obstacleGrid), len(obstacleGrid[0])
-        dmap = []
-        for i in range(m):
-            temp = [0] * n
-            dmap.append(temp)
-        for i in range(m):
-            if obstacleGrid[i][0] != 1:
-                dmap[i][0] = 1
-            else:
-                break
-        for j in range(n):
-            if obstacleGrid[0][j] != 1:
-                dmap[0][j] = 1
-            else:
-                break
-        for i in range(1, m):
-            for j in range(1, n):
+        if m == 0:
+            return 0
+        dmap = [[0] * (n + 1) for _ in range(m + 1)]
+        dmap[m - 1][n] = 1
+        for i in range(m - 1, -1, -1):
+            for j in  range(n - 1, -1, -1):
                 if obstacleGrid[i][j] == 1:
-                    continue
-                l = u = 0
-                if i - 1 >= 0:
-                    u = dmap[i - 1][j]
-                if j - 1 >= 0:
-                    l = dmap[i][j - 1]
-                dmap[i][j] = l + u
-        return dmap[m - 1][n - 1]
+                    dmap[i][j] = 0
+                else:
+                    dmap[i][j] = dmap[i][j + 1] + dmap[i + 1][j]
+        return dmap[0][0]