#include "shoes.h" long long count_swaps(std::vector<int> s) { int n = s.size() / 2; if (n == 1) return (s[0] > 0); bool samesize = true; for (int i = 0; i < 2 * n; i++) if (s[i] != s[0]) { samesize = false; break; } if (samesize) { std::vector<int> lefts; for (int i = 0; i < 2 * n; i++) if (s[i] < 0) lefts.push_back(i); int res = 0; for (int i = 0; i < n; i++) res += abs(lefts[i] - i * 2); return res; } return 1; }

shoes.cpp: In function 'long long int count_swaps(std::vector<int>)':
shoes.cpp:21:11: error: 'abs' was not declared in this scope
   21 |    res += abs(lefts[i] - i * 2);
      |           ^~~