diff --git a/04- April/25- Smallest Number in Infinite Set/25- Smallest Number in Infinite Set (Ahmed Gamal).cpp b/04- April/25- Smallest Number in Infinite Set/25- Smallest Number in Infinite Set (Ahmed Gamal).cpp
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+// Author: Ahmed Gamal
+
+// for this problem, we need to find the smallest number in an infinite set
+// as the infinite set consists of all the positive integers, we can use a variable to store the smallest number
+// we can use a boolean array to store the numbers that are in the set and the numbers that are not in the set
+// when we need to pop the smallest number, we can return the smallest number and mark it as not in the set
+// after that, we need to find the next smallest number in the set and update the smallest number
+// when we need to add a number to the set, we can mark it as in the set and update the smallest number if needed
+
+class SmallestInfiniteSet {
+    // N is the maximum number in the set
+    // sm is the smallest number in the set
+    // vis[i] is true if i is in the set and false otherwise
+    static const int N = 1e3 + 5;
+    int sm;
+    bool vis[N];
+public:
+    SmallestInfiniteSet() {
+        // initialize the smallest number to 1
+        // mark all the numbers as in the set
+        sm = 1;
+        memset(vis, true, sizeof vis);
+    }
+    
+    int popSmallest() {
+        // return the smallest number and mark it as not in the set
+        int x = sm;
+        vis[sm] = false;
+
+        // find the next smallest number in the set
+        while(not vis[sm]) {
+            sm++;
+        }
+
+        // return the answer
+        return x;
+    }
+    
+    void addBack(int num) {
+        // mark the number as in the set and update the smallest number if needed
+        vis[num] = true;
+        sm = min(sm, num);
+    }
+};
+
+/**
+ * Your SmallestInfiniteSet object will be instantiated and called as such:
+ * SmallestInfiniteSet* obj = new SmallestInfiniteSet();
+ * int param_1 = obj->popSmallest();
+ * obj->addBack(num);
+ */
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