Create 0397 Integer Replacement.md

Author: jjjllxx

greedy/0397 Integer Replacement.md

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+# 397. Integer Replacement
+https://leetcode-cn.com/problems/integer-replacement/  
+Given a positive integer n, you can apply one of the following operations:  
+If n is even, replace n with n / 2.  
+If n is odd, replace n with either n + 1 or n - 1.  
+Return the minimum number of operations needed for n to become 1.    
+
+Example 1:  
+Input: n = 8  
+Output: 3   
+Explanation: 8 -> 4 -> 2 -> 1  
+
+Example 2:  
+Input: n = 7  
+Output: 4    
+Explanation: 7 -> 8 -> 4 -> 2 -> 1  
+or 7 -> 6 -> 3 -> 2 -> 1  
+
+Example 3:  
+Input: n = 4  
+Output: 2  
+
+Constraints:   
+1 <= n <= 2^31 - 1   
+
+``` python3
+class Solution:
+    def integerReplacement(self, n: int) -> int:
+        ans=0
+        while n!=1:
+            if n%2==0:
+                n//=2
+                ans+=1
+            elif n%4==1:
+                n//=2
+                ans+=2
+            else:
+                if n==3:
+                    n=1
+                else:
+                    n=n//2+1
+                ans+=2
+        return ans
+```