牛客 字符串的转换路径问题

题目链接：https://www.nowcoder.com/practice/9939decf61a748d1877774095ecd5ed2?tpId=101&tqId=33191&tPage=1&rp=1&ru=/ta/programmer-code-interview-guide&qru=/ta/programmer-code-interview-guide/question-ranking

题目大意：

　　略。

分析：

　　先建图，然后 bfs 算每个节点到终点的最短距离，最后用 dfs 输出。

代码如下：

#include <bits/stdc++.h>
using namespace std;
 
#define INIT() ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define Rep(i,n) for (int i = 0; i < (int)(n); ++i)
#define For(i,s,t) for (int i = (int)(s); i <= (int)(t); ++i)
#define rFor(i,t,s) for (int i = (int)(t); i >= (int)(s); --i)
#define ForLL(i, s, t) for (LL i = LL(s); i <= LL(t); ++i)
#define rForLL(i, t, s) for (LL i = LL(t); i >= LL(s); --i)
#define foreach(i,c) for (__typeof(c.begin()) i = c.begin(); i != c.end(); ++i)
#define rforeach(i,c) for (__typeof(c.rbegin()) i = c.rbegin(); i != c.rend(); ++i)
 
#define pr(x) cout << #x << " = " << x << "  "
#define prln(x) cout << #x << " = " << x << endl
 
#define LOWBIT(x) ((x)&(-x))
 
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
#define UNIQUE(x) x.erase(unique(x.begin(), x.end()), x.end())
#define REMOVE(x, c) x.erase(remove(x.begin(), x.end(), c), x.end()); // 删去 x 中所有 c 
#define TOLOWER(x) transform(x.begin(), x.end(), x.begin(),::tolower);
#define TOUPPER(x) transform(x.begin(), x.end(), x.begin(),::toupper);
 
#define ms0(a) memset(a,0,sizeof(a))
#define msI(a) memset(a,0x3f,sizeof(a))
#define msM(a) memset(a,-1,sizeof(a))

#define MP make_pair
#define PB push_back
#define ft first
#define sd second
 
template<typename T1, typename T2>
istream &operator>>(istream &in, pair<T1, T2> &p) {
    in >> p.first >> p.second;
    return in;
}
 
template<typename T>
istream &operator>>(istream &in, vector<T> &v) {
    for (auto &x: v)
        in >> x;
    return in;
}

template<typename T>
ostream &operator<<(ostream &out, vector<T> &v) {
    Rep(i, v.size()) out << v[i] << " 
"[i == v.size() - 1];
    return out;
}
 
template<typename T1, typename T2>
ostream &operator<<(ostream &out, const std::pair<T1, T2> &p) {
    out << "[" << p.first << ", " << p.second << "]" << "
";
    return out;
}

inline int gc(){
    static const int BUF = 1e7;
    static char buf[BUF], *bg = buf + BUF, *ed = bg;
    
    if(bg == ed) fread(bg = buf, 1, BUF, stdin);
    return *bg++;
} 

inline int ri(){
    int x = 0, f = 1, c = gc();
    for(; c<48||c>57; f = c=='-'?-1:f, c=gc());
    for(; c>47&&c<58; x = x*10 + c - 48, c=gc());
    return x*f;
}

template<class T>
inline string toString(T x) {
    ostringstream sout;
    sout << x;
    return sout.str();
}

inline int toInt(string s) {
    int v;
    istringstream sin(s);
    sin >> v;
    return v;
}

//min <= aim <= max
template<typename T>
inline bool BETWEEN(const T aim, const T min, const T max) {
    return min <= aim && aim <= max;
}

typedef unsigned int uI;
typedef long long LL;
typedef unsigned long long uLL;
typedef vector< int > VI;
typedef vector< bool > VB;
typedef vector< char > VC;
typedef vector< double > VD;
typedef vector< string > VS;
typedef vector< LL > VL;
typedef vector< VI > VVI;
typedef vector< VB > VVB;
typedef vector< VS > VVS;
typedef vector< VL > VVL;
typedef vector< VVI > VVVI;
typedef vector< VVL > VVVL;
typedef pair< int, int > PII;
typedef pair< LL, LL > PLL;
typedef pair< int, string > PIS;
typedef pair< string, int > PSI;
typedef pair< string, string > PSS;
typedef pair< double, double > PDD;
typedef vector< PII > VPII;
typedef vector< PLL > VPLL;
typedef vector< VPII > VVPII;
typedef vector< VPLL > VVPLL;
typedef vector< VS > VVS;
typedef map< int, int > MII;
typedef unordered_map< int, int > uMII;
typedef map< LL, LL > MLL;
typedef map< string, int > MSI;
typedef map< int, string > MIS;
typedef multiset< int > mSI;
typedef multiset< char > mSC;
typedef set< int > SI;
typedef stack< int > SKI;
typedef deque< int > DQI;
typedef queue< int > QI;
typedef priority_queue< int > PQIMax;
typedef priority_queue< int, VI, greater< int > > PQIMin;
const double EPS = 1e-8;
const LL inf = 0x7fffffff;
const LL infLL = 0x7fffffffffffffffLL;
const LL mod = 1e9 + 7;
const int maxN = 5e3 + 7;
const LL ONE = 1;
const LL evenBits = 0xaaaaaaaaaaaaaaaa;
const LL oddBits = 0x5555555555555555;

struct Edge {
    int from;
    int to;
    
    Edge(int f, int t) : from(f), to(t){}
};

struct Vertex {
    int level;
    VI nexts;
    
    Vertex() {
        level = -1;
        nexts.clear();
    }
    
    void clear() {
        level = -1;
        nexts.clear();
    }
};

int N;
string S, T; 
int idxS, idxT;
string arr[maxN];
VVI ans;
VI res;

Vertex V[maxN];
vector< Edge > E;
bool vis[maxN];

void addEdge(Edge &x) {
    V[x.from].nexts.PB(E.size());
    E.PB(x);
}

void init() {
    ans.clear();
    res.clear();
    For(i, 1, N + 1) V[i].clear();
    E.clear();
}

int calc(string &x, string &y) {
    assert(x.size() == 3 && y.size() == 3);
    
    int cnt = 0;
    Rep(i, x.size()) if(x[i] != y[i]) ++cnt;
    return cnt;
}

bool cmp(const int &x, const int &y) {
    return arr[E[x].to] < arr[E[y].to];
}

void build() {
    For(i, 1, N) {
        For(j, i + 1, N) {
            int ret = calc(arr[i], arr[j]);
            
            if(ret == 1) {
                Edge t(i, j);
                addEdge(t);
                swap(t.from, t.to);
                addEdge(t);
            }
        }
    }
    
    For(i, 1, N) sort(ALL(V[i].nexts), cmp); // 为了按照字典序输出 
}

void bfs(int s) {
    ms0(vis);
    QI Q;
    Q.push(s);
    vis[s] = 1;
    
    int cnt = 1;
    int len = 1;
    
    while(!Q.empty()) {
        int tmp = Q.front(); Q.pop();
        --cnt;
        
        V[tmp].level = len;
        if(tmp == idxS) return;
        
        Rep(i, V[tmp].nexts.size()) {
            Edge &e = E[V[tmp].nexts[i]];
            
            if(vis[e.to]) continue;
            vis[e.to] = 1;
            Q.push(e.to);
        }
        
        if(cnt == 0) {
            cnt = Q.size();
            ++len;
        }
    }
}

void dfs(int s) {
    if(s == idxT) {
        ans.PB(res);
        return;
    }
    
    Rep(i, V[s].nexts.size()) {
        Edge &e = E[V[s].nexts[i]];
        
        if(V[e.to].level != V[s].level - 1) continue;
        res.PB(e.to);
        dfs(e.to);
        res.pop_back();
    }
}

void printAns() {
    if(ans.empty()) cout << "NO
";
    else {
        cout << "YES
";
        Rep(i, ans.size()) {
            Rep(j, ans[i].size()) {
                if(j) cout << " -> ";
                cout << arr[ans[i][j]];
            }
            cout << endl;
        }
    }
}

int main() {
    //freopen("MyOutput.txt","w",stdout);
    //freopen("input.txt","r",stdin);
    //INIT();
    while(cin >> N >> S >> T) {
        init();
        
        For(i, 1, N) { // 输入无重复 
            cin >> arr[i];
            if(T == arr[i]) idxT = i;
        }
        
        arr[++N] = S;
        idxS = N;
        build(); // 建图
        
        bfs(idxT); // bfs构建最短路路标 
        res.PB(idxS);
        dfs(idxS); // dfs按照路标输出最短路 
        
        printAns();
    }
    return 0;
}