Array: Find first duplicate value in C++ #1081

Author: Yashi11

Arrays/find_first_duplicate_value.cpp

@@ -0,0 +1,43 @@
+/*
+	Given an array of integers between 1 and n, inclusive, where n is the length of the array, write a function
+	that returns the first integer that appears more than once (when the array is read from left to right).
+
+	Sample Input = [2, 1, 5, 2, 3, 3, 4]
+	Output : 2
+
+	Please provide O(n) time and O(1) space solution along with O(n) time and O(n) space solution
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution{
+public:
+    // O(N) time complexity and O(N) Space Complexity Solution
+    int findDuplicate1(vector<int>& nums)
+    {
+        int N=nums.size();
+    
+        // Use Vector Instead of Unordered Set or Map for O(1) extraction time complexity
+        vector<bool> trk(N,false);
+    
+        for(int i=0;i<N;i++)
+        {
+            if(trk[nums[i]]==true) return nums[i];
+            trk[nums[i]]=true;
+        }
+        return -1;
+    }
+
+    // O(N) time complexity and O(1) Space Complexity Solution
+    int findDuplicate2(vector<int>& nums)
+    {
+        int N=nums.size();
+        for(int i=0;i<N;i++)
+        {
+            if(nums[abs(nums[i])]<0) return nums[i];
+            nums[abs(nums[i])]*=-1;
+        }
+        return -1;
+    }
+};