done 3 sorting problems

CSES - CSES Problem Set/Introducotry_Problems/Missing_Number.cpp

@@ -0,0 +1,23 @@
+//  Missing Number
+
+#include<bits/stdc++.h>
+
+using namespace std;
+
+int main() {
+    bitset<2 * (int)1e5> input;
+    int n; cin >> n;
+    for (int i{}; i < n; i++) {
+        int a; cin >> a;
+        input[a-1] = true;
+    }
+    input = ~input;
+    for (int i = 0; i < n; i++) {
+        if (input[i]) {
+            cout << i + 1<< endl;
+            break;
+        }
+    }
+    return 0;
+
+}