chore(CPlusPlus): add three sum (#595)

Co-authored-by: Ming Tsai <37890026+ming-tsai@users.noreply.github.com>

algorithms/CPlusPlus/Arrays/three-sum.cpp

@@ -0,0 +1,102 @@
+//Description :c++ solution to find all the unique triplet without using any extra space.
+//using this method we will be able to find all the unique triplets 
+//Time Complexity : O(n), where n is the array size
+//Space Complexity : O(1),it will take only constant amount of time.
+//sample 
+// input 1: arr[]=[-1,0,1,2,-1,4]
+//output 1:[[-1,0,1][-1,-1,2]]
+//input 2:arr[]=[]
+//output 2:[]
+
+#include<bits/stdc++.h>
+using namespace std;
+
+    void findTriplet(int arr[],int n,int sum) {
+    
+	int i;
+ 
+    // Sort the input array
+    sort(arr, arr + n);
+ 
+    // For handling the cases when no such
+    // triplets exits.
+    bool flag = false;
+ 
+    // Iterate over the array from start to n-2.
+    for (i = 0; i < n - 2; i++)
+    {
+        if (i == 0 || arr[i] > arr[i - 1])
+        {
+            // Index of the first element in
+            // remaining range.
+            int start = i + 1;
+ 
+            // Index of the last element
+            int end = n - 1;
+ 
+            // Setting our new target
+            int target = sum - arr[i];
+ 
+            while (start < end)
+            {
+                // Checking if current element
+                // is same as previous
+                if (start > i + 1
+                    && arr[start] == arr[start - 1])
+                {
+                    start++;
+                    continue;
+                }
+ 
+                // Checking if current element is
+                // same as previous
+                if (end < n - 1
+                    && arr[end] == arr[end + 1])
+                {
+                    end--;
+                    continue;
+                }
+ 
+                // If we found the triplets then print it
+                // and set the flag
+                if (target == arr[start] + arr[end])
+                {
+                    cout << "[" << arr[i]
+                         << "," << arr[start]
+                         << "," << arr[end] << "] ";
+                    flag = true;
+                    start++;
+                    end--;
+                }
+                // If target is greater then
+                //  increment the start index
+                else if (target > (arr[start] + arr[end]))
+                {
+                    start++;
+                }
+                // If target is smaller than
+                // decrement the end index
+                else {
+                    end--;
+                }
+            }
+        }
+    }
+ 
+    // If no such triplets found
+    if (flag == false) {
+        cout << "No Such Triplets Exist"
+             << "\n";
+    }
+	
+}
+int main()
+{
+//	int arr[]={12,3,6,1,6,9};
+int arr[]={-1,0,1,2,-1,-4};
+	int n=sizeof(arr)/sizeof(arr[0]);
+	int sum=0;
+	findTriplet(arr,n,sum);
+	return 0;
+	
+}

algorithms/CPlusPlus/README.md

@@ -25,7 +25,7 @@
 - [Index of Smallest element of Array](Arrays/index-of-smallest-element-of-array.cpp)
 - [Move Zeros to End of The Array](Arrays/move-zeros-to-end-of-array.cpp)
 - [Kadane's Algorithm](Arrays/Kadane's-Algorithm.cpp)
-
+- [All unique triplet that sum up to given value](Arrays/three-sum.cpp)
 
 ## Dynamic-Programming