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  1. #include <iostream>
  2. #include <vector>
  3.  
  4. int find_missing(std::vector<int>& v)
  5. {
  6.     for (std::size_t i = 0; i != v.size(); ++i) {
  7.  
  8.         std::size_t e = i;
  9.  
  10.         while (0 < v[e]
  11.             && std::size_t(v[e]) <= v.size()
  12.             && std::size_t(v[e]) != e + 1
  13.             && v[e] != v[v[e] - 1]
  14.         ) {
  15.             std::swap(v[e], v[v[e] - 1]);
  16.         }
  17.     }
  18.     for (std::size_t i = 0; i != v.size(); ++i) {
  19.         if (std::size_t(v[i]) != i + 1) {
  20.             return i + 1;   
  21.         }
  22.     }
  23.     return v.size();
  24. }
  25.  
  26. int main()
  27. {
  28.     std::vector<int> v = {3, 4, -1, 1};
  29.     std::cout << find_missing(v) << std::endl;
  30.     v = {1, 2, 0};
  31.     std::cout << find_missing(v) << std::endl;
  32.     v = {2, 2, 2};
  33.     std::cout << find_missing(v) << std::endl;
  34. }
  35.  
Success #stdin #stdout 0s 4488KB
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https://ideone.com/mpjJxt
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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