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C++/MEX.cpp

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+
+#include <bits/stdc++.h>
+using namespace std;
+
+#define MAXN 100001
+
+void constructMEX(int arr[], int N)
+{
+
+    int hash[MAXN] = { 0 };
+
+
+    for (int i = 0; i < N; i++) {
+
+        hash[arr[i]] = 1;
+    }
+
+
+    int MexOfArr;
+
+    // Find MEX of arr[]
+    for (int i = 1; i < MAXN; i++) {
+        if (hash[i] == 0) {
+            MexOfArr = i;
+            break;
+        }
+    }
+
+    // Stores MEX for all indices
+    int B[N];
+
+    // Traverse the given array
+    for (int i = 0; i < N; i++) {
+
+        // Update MEX
+        if (arr[i] < MexOfArr)
+            B[i] = arr[i];
+
+        // MEX default
+        else
+            B[i] = MexOfArr;
+    }
+
+    // Print the array B
+    for (int i = 0; i < N; i++)
+        cout << B[i] << ' ';
+}
+
+// Driver Code
+int main()
+{
+    // Given array
+    int arr[] = { 2, 1, 5, 3 };
+
+    // Given size
+    int N = sizeof(arr)
+            / sizeof(arr[0]);
+
+    // Function call
+    constructMEX(arr, N);
+    return 0;
+}