diff --git a/Find the element that appears once in an array where every other element appears twice b/Find the element that appears once in an array where every other element appears twice
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+++ b/Find the element that appears once in an array where every other element appears twice	
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+// C++ program to find
+// element that appears once
+#include <bits/stdc++.h>
+
+using namespace std;
+
+// function which find number
+int singleNumber(int nums[],int n)
+{
+	map<int,int> m;
+	long sum1 = 0,sum2 = 0;
+
+	for(int i = 0; i < n; i++)
+	{
+		if(m[nums[i]] == 0)
+		{
+			sum1 += nums[i];
+			m[nums[i]]++;
+		}
+		sum2 += nums[i];
+	}
+	
+	// applying the formula.
+	return 2 * (sum1) - sum2;
+}
+
+// Driver code
+int main()
+{
+	int a[] = {2, 3, 5, 4, 5, 3, 4};
+	int n = 7;
+	cout << singleNumber(a,n) << "\n";
+
+	int b[] = {15, 18, 16, 18, 16, 15, 89};
+
+	cout << singleNumber(b,n);
+	return 0;
+}
+
+// This code is contributed by mohit kumar 29