add prob #397(2nd); O(logN) in time and O(1) in space

Author: randomwalk10

397_Integer_Replacement_2nd.cpp

@@ -0,0 +1,30 @@
+/* O(logN) in time and O(1) in space */
+
+class Solution {
+public:
+    int integerReplacement(int n) {
+		int cnt = 0;
+		while(n>1){
+			if((n&0b1)==0){
+				n >>= 1;
+				++cnt;
+			}
+			else{
+				if((n&0b11)==0b01){
+					n >>= 2;
+					cnt += 3; // reduction, divide, divide
+				}
+				else if(n==0b11){
+					n >>= 1;
+					cnt += 2; // reduction, divide
+				}
+				else{
+					n >>= 2;
+					++n;
+					cnt += 3; // addition, divide, divide
+				}
+			}
+		}
+		return cnt;
+    }
+};