Added top-down DP for unique paths ii

Author: shichao-an

unique_paths_ii/solution2.py

@@ -0,0 +1,34 @@
+class Solution:
+    # @param obstacleGrid, a list of lists of integers
+    # @return an integer
+    def uniquePathsWithObstacles(self, obstacleGrid):
+        n = len(obstacleGrid)
+        m = len(obstacleGrid[0])
+        t = [[-1 for i in range(m)] for j in range(n)]
+        return self.unique_paths(obstacleGrid, m - 1, n - 1, t)
+
+    def unique_paths(self, grid, x, y, t):
+        if x == 0 and y == 0:
+            return 1 if grid[y][x] == 0 else 0
+        elif t[y][x] != -1:
+            return t[y][x]
+        elif x > 0 and y == 0:
+            if grid[y][x] == 1:
+                t[y][x] = 0
+            else:
+                t[y][x] = self.unique_paths(grid, x - 1, y, t)
+            return t[y][x]
+        elif y > 0 and x == 0:
+            if grid[y][x] == 1:
+                t[y][x] = 0
+            else:
+                t[y][x] = self.unique_paths(grid, x, y - 1, t)
+            return t[y][x]
+        else:
+            if grid[y][x] == 1:
+                t[y][x] = 0
+            else:
+                a = self.unique_paths(grid, x - 1, y, t)
+                b = self.unique_paths(grid, x, y - 1, t)
+                t[y][x] = a + b
+            return t[y][x]