P1032 字串变换

bfs，把能换的全部换掉然后入队即可。

#include<iostream>
#include<map>
#include<unordered_map>
#include<queue>
#include<vector>

using namespace std;

#define PSI pair<string, int>
#define PSS pair<string, string>

vector<PSS> ss;
unordered_map<string, int> st;

string a, b;

vector<int> find(const string &a, const string &b){
    vector<int> res;
    int j = 0;
    for(int i = 0; i < a.size(); i ++){
        if(j == b.size()) res.push_back(i - j);
        if(j < b.size() && a[i] == b[j]) j ++;
        else i = i - j, j = 0;
    }
    
    if(j == b.size()) res.push_back(a.size() - j);
    
    return res;
}

int bfs(){
    queue<PSI> q;
    
    q.push({a, 0});
    
    while(q.size()){
        auto h = q.front();
        q.pop();
        
        for(auto t : ss){
            vector<int> k = find(h.first, t.first);
            
            for(int i = 0; i < k.size(); i ++){
                string temp = h.first;
                temp = temp.replace(k[i], t.first.size(), t.second);
                if(st[temp] == 0){
                    st[temp] = 1;
                    q.push({temp, h.second + 1});
                
                    if(temp == b || h.second + 1 > 10) return h.second + 1;
                }
            }
        }
    }
}

int main(){
    cin >> a >> b;
    
    string p, q;
    while(cin >> p >> q) ss.push_back({p, q});
    
    int k = bfs();
    
    if(k > 10) puts("NO ANSWER!");
    else cout << k << endl;
    
    return 0;
}