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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5.     ios::sync_with_stdio(false);
  6.     cin.tie(nullptr);
  7.     int N; 
  8.     if(!(cin >> N)) return 0;
  9.     long long best1 = LLONG_MIN, cur1 = 0; // Kadane on B
  10.     long long best2 = LLONG_MIN, cur2 = 0; // Kadane on -B
  11.     for (int i = 1; i <= N; ++i) {
  12.         long long a; cin >> a;
  13.         long long Bi = (i & 1) ? a : -a;   // B_i
  14.         long long nBi = -Bi;               // -B_i == C_i
  15.  
  16.         // Kadane for B
  17.         cur1 = max(Bi, cur1 + Bi);
  18.         best1 = max(best1, cur1);
  19.  
  20.         // Kadane for -B
  21.         cur2 = max(nBi, cur2 + nBi);
  22.         best2 = max(best2, cur2);
  23.     }
  24.     cout << max(best1, best2) << "\n";
  25.     return 0;
  26. }
Success #stdin #stdout 0s 5324KB
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stdin
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5
-1 2 -4 -2 3
stdout
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7
https://ideone.com/Vjuk9R
language:
C++ (gcc 8.3)
created:
3 days ago
visibility:
public

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