C++ 异或：异或同一个数2次或者偶数次，那么本身的值不变。 #include <iostream> using namespace std; int main(){ int N; int sum = 0; cin >> N; for(int i = 1; i <= N; i++){ sum ^= i; } int num; for(int i = 1; i <= N - 1; i++){ cin >> num; sum ^= num; } cout <<...

int main() { int n, a; while (cin >> n) { long long sum = 0; for (int i = 1; i <= n; i++)sum += i; for (int i = 0; i < n - 1; i++) { cin >> a; sum -= a; } cout << sum << endl; } }