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  1. #include <iostream>
  2. #include <vector>
  3. #include <unordered_map>
  4. using namespace std;
  5.  
  6. int maxLength(vector<int>& arr) {
  7.     int n = arr.size();
  8.  
  9.     // prefixSum -> first index
  10.     unordered_map<int, int> firstSeen; 
  11.     int prefixSum = 0;
  12.     int maxLen = 0;
  13.  
  14.     // insert prefix sum 0 at index -1
  15.     // to handle sum from start
  16.     firstSeen[0] = -1;
  17.  
  18.     for (int i = 0; i < n; i++) {
  19.         prefixSum += arr[i];
  20.  
  21.         // prefix sum has been seen before
  22.         if (firstSeen.find(prefixSum) != firstSeen.end()) {
  23.             int prevIndex = firstSeen[prefixSum];
  24.             int length = i - prevIndex;
  25.             maxLen = max(maxLen, length);
  26.         }
  27.         else {
  28.  
  29.             // Store first occurrence of this prefix sum
  30.             firstSeen[prefixSum] = i;
  31.         }
  32.     }
  33.  
  34.     return maxLen;
  35. }
  36.  
  37. int main() {
  38.     vector<int> arr = {15, -2, 2, -8, 1, 7, 10};
  39.     cout << maxLength(arr) << endl;
  40.     return 0;
  41. }
Success #stdin #stdout 0s 5320KB
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https://ideone.com/t1SI7Z
language:
C++ (gcc 8.3)
created:
21 hours ago
visibility:
public

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