Create integer-replacement.cpp

Author: kamyu104

C++/integer-replacement.cpp

@@ -0,0 +1,55 @@
+// Time:  O(logn)
+// Space: O(1)
+
+// Iterative solution.
+class Solution {
+public:
+    int integerReplacement(int n) {
+        if (n == 2147483647) {
+            return 2 + integerReplacement(n / 2 + 1);
+        }
+
+        int result = 0;
+        while (n != 1) {
+            const auto b = n & 3;
+            if (n == 3) {
+                --n;
+            } else if (b == 3) {
+                ++n;
+            } else if (b == 1) {
+                --n;
+            } else {
+                n /= 2;
+            }
+            ++result;
+        }
+        return result;
+    }
+};
+
+// Time:  O(logn)
+// Space: O(logn)
+// Recursive solution
+class Solution2 {
+public:
+    int integerReplacement(int n) {
+        if (n == 2147483647) {
+            return 2 + integerReplacement(n / 2 + 1);
+        }
+
+        if (n < 4) {
+            switch (n % 4) {
+                case 0: case 1: return 0;
+                case 2: return 1;
+                case 3: return 2;
+            }
+        }
+
+        switch (n % 4) {
+            case 0: case 2: return integerReplacement(n / 2) + 1;
+            case 1: return integerReplacement((n - 1) / 4) + 3;
+            case 3: return integerReplacement((n + 1) / 4) + 3;
+        }
+        return 0;
+    }
+};