70

Author: tech-cow

README.md

@@ -101,3 +101,9 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |39|[Combination Sum](https://leetcode.com/problems/combination-sum/#/description)| [Python [Yu]](./backtrack/Yu/39.py) | _O(K * (2^N)_| _O(N)_  | Medium | |[公瑾讲解](https://youtu.be/HdS5dOaz-mk)|
 |40|[Combination Sum II](https://leetcode.com/problems/combination-sum-ii/#/solutions)| [Python [Yu]](./backtrack/Yu/39.py) | _O(K * (2^N)_| _O(N)_  | Medium | |[公瑾讲解](https://youtu.be/HdS5dOaz-mk)|
 |216|[Combination Sum III](https://leetcode.com/problems/combination-sum-iii/#/description)| [Python [Yu]](./backtrack/Yu/216.py) | _O(K * (2^N)_| _O(N)_  | Medium | ||
+
+
+## Dynamic Programming Easy
+|  #  | Title | Solution | Time | Space | Difficulty | Note|
+|-----|-------| -------- | ---- | ------|------------|-----|
+|70|[Climbing Stairs](https://leetcode.com/problems/climbing-stairs/#/solutions)| [Python [Yu]](./backtrack/Yu/216.py) | _O(N)_| _O(1)_  | Easy| |

dp/70.py

@@ -0,0 +1,66 @@
+# 70. Climbing Stairs
+# Author: Yu Zhou
+
+# Each time you can either climb 1 or 2 steps.
+# 各种方法
+# Bottom Up就是从最基本的base case然后慢慢的解决所有的subproblem，指导累计至N
+# 这道题因为只Care  N-1 和 N-2 两个值
+# 可以直接用O(1)的Space，具体操作就是对两个函数进行更改，而不是存Hash或者Array
+
+
+# Top Down Recursion (超时)
+class Solution(object):
+    def climbStairs(self, n):
+      # Base case:
+      if n == 1:
+        return 1
+      if n == 2:
+        return 2
+      return self.climbStairs(n-1) + self.climbStairs(n-2)
+
+# Top Down Memorization DP (Hash表)
+class Solution(object):
+    def __init__(self):
+        self.hash = {1:1, 2:2}
+
+    def climbStairs(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        if n not in self.hash:
+            self.hash[n] = self.climbStairs(n-1) + self.climbStairs(n-2)
+        return self.hash[n]
+
+# Bottom-up DP (ArrayList)
+class Solution(object):
+    def climbStairs(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        if n == 1:
+            return 1
+
+        res = [1,2]
+        for i in xrange(2, n):
+            res.append(res[i-1] + res[i-2])
+        return res[-1]
+
+# Bottom-up DP (Constant)
+class Solution(object):
+    def climbStairs(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        if n == 1:
+            return 1
+
+        a, b = 1, 2
+        for i in xrange(2, n):
+            temp = b
+            b = b + a
+            a = temp
+
+        return b

try.py

@@ -1,7 +1,4 @@
-# Creates a list containing 5 lists, each of 8 items, all set to 0
-n = 6;
-Matrix = [["." for x in range(n)] for y in range(n)]
-string = ','.join(Matrix)
-
-#print Matrix
-print string
+lst = [[0] * 3 for _ in xrange(2)]
+ret = ', '.join(str(x) for x in lst)
+print (str(lst))
+print ret