第二题答案，可能不是最终答案，但整体思路没动过 #include <iostream> #include <vector> #include <unordered_map> #include <cmath> #define LL long long using namespace std; int main() { int n; cin >> n; vector<unordered_map<int,int>> t(9, unordered_map<int,int>()); vector<int> nums; for (int i = 0; i < n; ++i) { LL x; cin >> x; nums.push_back(x); LL base = 10; for (int j = 0; j < 9; ++j) { t[j][int((LL)(x)*(LL)(base) % (LL)(7))]++; base *= 10; } } int cnt = 0; for (int i = 0; i < n; ++i) { int base = 0; int x = nums[i]; do { base++; x /= 10; } while (x > 0); int remain = (7 - nums[i] % 7) % 7; if (t[base-1][remain] >= 2) if (((LL)(nums[i]) * (LL)(pow(10, base))) % 7 == remain) { cnt += t[base - 1][remain] - 1; } else cnt += t[base - 1][remain]; else if (t[base-1][remain] < 1) continue; else { if (((LL)(nums[i]) * (LL)(pow(10, base))) % 7 == remain) { continue; } else cnt++; } } cout << cnt << endl; return 0; }