Added solution

Author: avidLearnerInProgress

amazon/zero_sum_subarrays.cpp

@@ -0,0 +1,77 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+int mod=1e9+7;
+#define F(a,b,var) for(int var=a;var<b;var++)
+#define FAST_INP  ios_base::sync_with_stdio(false);cin.tie(NULL)
+
+/*
+You are given an array A of size N. 
+You need to print the total count of sub-arrays having their sum equal to 0
+For each test case, in a new line, print the total number of subarrays whose sum is equal to 0.
+
+Constraints:    
+1 <= T <= 100
+1<= N <= 107
+-1010 <= Ai <= 1010
+
+Example:
+Input:
+2
+6
+0 0 5 5 0 0
+10
+6  -1 -3 4 -2 2 4 6 -12 -7
+
+Output:
+6
+4
+*/
+
+
+int main()
+ {
+	//code
+	
+        FAST_INP;
+        int T;
+        cin>>T;
+        while(T--)
+        {   
+            int n, c; cin>>n;
+            vector<int> sub_array_test;
+            for(int i = 0; i < n; i++){
+                int curr;
+                cin>>curr;
+                sub_array_test.push_back(curr);
+            }
+            
+            
+            /*
+            maintain global sum = 0
+            use hashmap that maps the current sum to vector of pairs or end index... map<int, vector<int>>
+        
+            if sum(arr[0...i]) == 0 and sum(arr[0...j]) == 0
+            then there exists a sub-array arr[i+1]...arr[j] whose sum is 0
+            */
+            // initialisations
+            
+            unordered_map<int, int> sub_array_mp;
+            int curr_sum = 0, zero_count = 0;
+            
+            //o(n)
+            for(int i = 0; i < sub_array_test.size(); i++){
+                curr_sum += sub_array_test[i]; //cummulative sum
+                
+                if(curr_sum == 0) // indicates that there exists a pair from 0 to i
+                        zero_count++;
+    
+                if(sub_array_mp[curr_sum] != 0) // a pair exists whose sum == 0 is already discovered
+                    zero_count += sub_array_mp[curr_sum];                    
+                
+                sub_array_mp[curr_sum]++;
+            }
+            cout<<zero_count<<"\n"; 
+        }
+	return 0;
+}