Added 3Sum.cpp (div-bargali#113)

Author: Anjalikamath

C++/Algorithms/3Sum.cpp

@@ -0,0 +1,54 @@
+/*
+Given an array of n integers, are there elements a, b, c in nums such that a + b + c = 0? 
+Find all unique triplets in the array which gives the sum of zero.
+Notice that the solution set must not contain duplicate triplets.
+*/
+
+/* Sample inputs and outputs
+Input: arr = [-1,0,1,2,-1,-4]
+Output: [-1,-1,2] [-1,0,1]
+
+Input: arr= [0]
+Output: []
+*/
+
+#include <iostream>
+#include <bits/stdc++.h>
+using namespace std;
+
+
+//Function to check if triplet with sum = 0 exists
+void threeSum(int arr[],int n) {
+ 
+ sort(arr,arr + n);
+ for(int i = 0; i < n; i++)
+ {
+ if(i != 0 && arr[i] == arr[i-1])continue;
+ int j = i+1, k = n-1;
+ while(j < k)
+ {
+ int sum = arr[i] + arr[j] + arr[k];
+ if(sum == 0)
+ {
+ cout<<"[ "<<arr[i]<<", "<<arr[j]<<", "<<arr[k]<<"] ";
+ j++;
+ while (j < k && arr[j] == arr[j-1]) j++;
+ 
+ }
+ else if (sum > 0) k--;
+ else j++;
+ }
+ }
+ 
+}
+
+//Driver code to test the threeSum function
+int main(){
+
+ int arr[]={ -1, 0, 1, 2, -1, -4 };
+ int n = 6;
+ 
+ threeSum(arr,n);
+
+ return 0;
+}