Subarray with 0 sum

Author: sachuverma

DSA Crack Sheet/README.md

@@ -21,6 +21,7 @@
 - [Count pairs with given sum](https://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum5022/1# "view question") - [Cpp Solution](./solutions/Count%20pairs%20with%20given%20sum.cpp)
 - [Common elements](https://practice.geeksforgeeks.org/problems/common-elements1132/1# "view question") - [Cpp Solution](./solutions/Common%20elements.cpp)
 - [Rearrange array in alternating positive & negative items with O(1) extra space](https://www.geeksforgeeks.org/rearrange-array-alternating-positive-negative-items-o1-extra-space/ "view topic") - [Cpp Solution](./solutions/Rearrange%20array%20in%20alternating%20positive%20&%20negative%20items%20with%20O(1)%20extra%20space.cpp)
+- [Subarray with 0 sum](https://practice.geeksforgeeks.org/problems/subarray-with-0-sum-1587115621/1# "view question") - [Cpp Solution](./solutions/Subarray%20with%200%20sum.cpp)
 - []( "view question") - [Cpp Solution](./solutions/.cpp)
 
 <!-- - []( "view question") - [Cpp Solution](./solutions/) -->

DSA Crack Sheet/solutions/Subarray with 0 sum.cpp

@@ -0,0 +1,52 @@
+/*
+Subarray with 0 sum
+====================
+
+Given an array of positive and negative numbers. Find if there is a subarray (of size at-least one) with 0 sum.
+
+Example 1:
+Input:
+5
+4 2 -3 1 6
+Output: 
+Yes
+Explanation: 
+2, -3, 1 is the subarray 
+with sum 0.
+
+Example 2:
+Input:
+5
+4 2 0 1 6
+Output: 
+Yes
+Explanation: 
+0 is one of the element 
+in the array so there exist a 
+subarray with sum 0.
+Your Task:
+You only need to complete the function subArrayExists() that takes array and n as parameters and returns true or false depending upon whether there is a subarray present with 0-sum or not. Printing will be taken care by the drivers code.
+
+Expected Time Complexity: O(n).
+Expected Auxiliary Space: O(n).
+
+Constraints:
+1 <= N <= 104
+-105 <= a[i] <= 105
+*/
+
+bool subArrayExists(int arr[], int n)
+{
+  unordered_set<int> prefix_sums;
+  int sum = 0;
+  for (int i = 0; i < n; ++i)
+  {
+    sum += arr[i];
+    if (!sum)
+      return true;
+    if (prefix_sums.find(sum) != prefix_sums.end())
+      return true;
+    prefix_sums.insert(sum);
+  }
+  return false;
+}