贪心去做 #include <bits/stdc++.h> using namespace std; typedef long long ll; int main() { ll n, tmp; vector<int> cnt(10); vector<int> s; vector<int> vis(10); cin >> n; tmp = n; while(tmp > 0) { cnt[tmp%10]++; s.push_back(tmp%10); tmp /= 10; } reverse(s.begin(), s.end()); stack<int> st; for (int i = 0; i < s.size(); ++i) { //cout << s[i] << endl; cnt[s[i]]--; if (st.empty()) { st.push(s[i]); vis[s[i]] = 1; } else { while(!st.empty() && st.top() < s[i] && cnt[st.top()] && !vis[s[i]]) { vis[st.top()] = 0; st.pop(); } if (!vis[s[i]]) st.push(s[i]), vis[s[i]] = 1; } } ll ans = 0, T = 1; while (!st.empty()) { ll x = st.top();st.pop(); ans += x*T; T *= 10; } cout << ans << endl; return 0; }