Merge pull request #15 from offamitkumar/11-add-problem-120

adds problem 120

Author: offamitkumar

Diff for: README.md

@@ -749,6 +749,11 @@ def __init__(self, val, left=None, right=None):
 #### Click [__*here*__](Solution/Day-119.cpp) for solution.
 #### Click [__*here*__](https://leetcode.com/problems/squares-of-a-sorted-array/) to visit [*LeetCode*](https://leetcode.com/) for this question.
 ---
+## Problem 120
+##### This problem was asked by Microsoft.
+##### Implement the singleton pattern with a twist. First, instead of storing one instance, `store two instances`. And in every `even` call of `getInstance()`, return the `first instance` and in every `odd call` of getInstance(), return the `second instance`.
+#### Click [__*here*__](Solution/Day-120.cpp) for solution.
+---
 ## Problem 122 
 ##### This question was asked by Zillow.
 ##### You are given a 2-d matrix where each cell represents number of coins in that cell. Assuming we start at matrix[0][0], and can only move right or down, find the maximum number of coins you can collect by the bottom right corner.

Diff for: Solution/Day-120.cpp

@@ -0,0 +1,59 @@
+//
+// Created by Amit Kumar on 12/07/23.
+//
+
+#include "iostream"
+#include "string"
+
+using namespace std;
+
+enum State {
+    NotInitialized, Odd, Even
+};
+
+class ModifiedSingleton {
+
+    string instanceName;
+
+    ModifiedSingleton() = default;
+
+    explicit ModifiedSingleton(string name) : instanceName(std::move(name)) {}
+
+public:
+    ModifiedSingleton(ModifiedSingleton &ms) = delete;
+
+    static ModifiedSingleton &getInstance() {
+        static ModifiedSingleton instanceOne;
+        static ModifiedSingleton instanceTwo;
+
+        static State currentState = State::NotInitialized;
+
+        if (currentState == State::NotInitialized) {
+            currentState = State::Odd;
+            instanceOne = ModifiedSingleton("First Instance");
+            instanceTwo = ModifiedSingleton("Second Instance");
+        }
+
+        if (currentState == State::Odd) {
+            currentState = State::Even;
+            return instanceTwo;
+        } else {
+            currentState = State::Odd;
+            return instanceOne;
+        }
+    }
+
+    friend ostream &operator<<(ostream &out, const ModifiedSingleton &ms) {
+        out << ms.instanceName;
+        return out;
+    }
+
+};
+
+int main() {
+    for (int i = 1; i < 10; ++i) {
+        cout << ((i&1) ? "Odd Call: " : "Even Call: ");
+        cout << ModifiedSingleton::getInstance() << endl;
+    }
+    return 0;
+}