Create 70_Climbing_Stairs.md

Author: koji

70_Climbing_Stairs.md

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+## 70. Climbing Stairs
+
+
+You are climbing a staircase. It takes n steps to reach the top.
+
+Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
+
+ 
+
+Example 1:
+
+Input: n = 2
+Output: 2
+Explanation: There are two ways to climb to the top.
+1. 1 step + 1 step
+2. 2 steps
+Example 2:
+
+Input: n = 3
+Output: 3
+Explanation: There are three ways to climb to the top.
+1. 1 step + 1 step + 1 step
+2. 1 step + 2 steps
+3. 2 steps + 1 step
+ 
+
+Constraints:
+
+1 <= n <= 45
+
+
+```python
+def climbStairs(self, n: int) -> int:
+ 
+ dp = [0] * (n+1)
+ dp[0] = 1
+ dp[1] = 1
+ for i in range(2, n+1):
+ dp[i] = dp[i-1] + dp[i-2]
+ return dp[-1]
+```
+
+```
+Runtime: 20 ms, faster than 98.10% of Python3 online submissions for Climbing Stairs.
+Memory Usage: 14.3 MB, less than 10.74% of Python3 online submissions for Climbing Stairs.
+```