add solution: unique-paths

Author: dusunax

unique-paths/dusunax.py

@@ -0,0 +1,21 @@
+'''
+# 62. Unique Paths
+
+use dynamic programming & a dp table to store the number of ways to reach each cell.
+
+### TC is O(m * n):
+- iterating through every cell in the grid. = O(m * n)
+- updating each cell in the grid. = O(1)
+
+### SC is O(m * n):
+- using a dp table (2D array) to store the number of ways to reach each cell. = O(m * n)
+'''
+class Solution:
+    def uniquePaths(self, m: int, n: int) -> int:
+        dp = [[1] * n for _ in range(m)]
+
+        for y in range(1, m):
+            for x in range(1, n):
+                dp[y][x] = dp[y - 1][x] + dp[y][x - 1]
+
+        return dp[m - 1][n - 1]