[hdu2112]最短路

相当于模板题了，用trie来完成字符串到数字的映射比map<string, int>要快不少，令外可以考虑hash。

运行时间对比：

(1)(2)600ms左右 (3)3000ms左右(4)1500ms左右

（1）O(n^2)的dijkstra:

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#include <stdio.h> #include <string.h> #include <iostream> #include <algorithm> #include <vector> #include <queue> #include <set> #include <map> #include <string> #include <math.h> #include <stdlib.h> #include <time.h> #include <map> using namespace std; #define umin(a, b) if ((a) > (b)) (a) = (b) const int maxn = 157; int n; struct Trie { int ch[maxn * 32][26]; int val[maxn * 32], sz; void init() { memset (val, 0, sizeof (val)); memset (ch[0], 0, sizeof (ch[0])); sz = 0; } int insert( char *s) { int i = 0, j = 0; for (; s[j]; i = ch[i][s[j]], j ++) { if (s[j] < 'a' ) s[j] -= 'A' ; else s[j] -= 'a' ; if (!ch[i][s[j]]) { ch[i][s[j]] = ++ sz; memset (ch[sz], 0, sizeof (ch[sz])); } } if (!val[i]) val[i] = ++ n; return val[i]; } } trie; int dist[maxn][maxn], d[maxn]; bool vis[maxn]; int main() { #ifndef ONLINE_JUDGE freopen ( "in.txt" , "r" , stdin); #endif // ONLINE_JUDGE int m; char s1[40], s2[40]; int t; while (cin >> m, ~m) { n = 0; trie.init(); scanf ( "%s%s" , s1, s2); trie.insert(s1); t = trie.insert(s2); memset (dist, 0x3f, sizeof (dist)); for ( int i = 0; i < m; i ++) { int x; scanf ( "%s%s%d" , s1, s2, &x); int u = trie.insert(s1), v = trie.insert(s2); umin(dist[u][v], x); umin(dist[v][u], x); } memset (vis, 0, sizeof (vis)); memset (d, 0x3f, sizeof (d)); d[1] = 0; for ( int i = 1; i < n; i ++) { int pos = 0, mind = 0x3f3f3f3f; for ( int j = 1; j <= n; j ++) { if (!vis[j] && d[j] < mind) { mind = d[j]; pos = j; } } if (!pos) break ; vis[pos] = true ; for ( int j = 1; j <= n; j ++) { if (!vis[j]) umin(d[j], d[pos] + dist[pos][j]); } } printf ( "%d\n" , d[t] == 0x3f3f3f3f? -1 : d[t]); } return 0; }

（2）SPFA:

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#include <stdio.h> #include <string.h> #include <iostream> #include <algorithm> #include <vector> #include <queue> #include <set> #include <map> #include <string> #include <math.h> #include <stdlib.h> #include <time.h> #include <map> using namespace std; #define umin(a, b) if ((a) > (b)) (a) = (b) const int maxn = 157; int n; struct Trie { int ch[maxn * 32][26]; int val[maxn * 32], sz; void init() { memset (val, 0, sizeof (val)); memset (ch[0], 0, sizeof (ch[0])); sz = 0; } int insert( char *s) { int i = 0, j = 0; for (; s[j]; i = ch[i][s[j]], j ++) { if (s[j] < 'a' ) s[j] -= 'A' ; else s[j] -= 'a' ; if (!ch[i][s[j]]) { ch[i][s[j]] = ++ sz; memset (ch[sz], 0, sizeof (ch[sz])); } } if (!val[i]) val[i] = ++ n; return val[i]; } } trie; vector<vector< int > >G, W; queue< int > Q; int d[maxn]; bool mark[maxn]; bool relax( int u, int v, int w) { if (d[v] > d[u] + w) { d[v] = d[u] + w; return true ; } return false ; } int main() { #ifndef ONLINE_JUDGE freopen ( "in.txt" , "r" , stdin); #endif // ONLINE_JUDGE int m; char s1[40], s2[40]; int t; while (cin >> m, ~m) { n = 0; trie.init(); scanf ( "%s%s" , s1, s2); trie.insert(s1); t = trie.insert(s2); G.clear(); W.clear(); G.resize(maxn + 2); W.resize(maxn + 2); for ( int i = 0; i < m; i ++) { int x; scanf ( "%s%s%d" , s1, s2, &x); int u = trie.insert(s1), v = trie.insert(s2); G[u].push_back(v); G[v].push_back(u); W[u].push_back(x); W[v].push_back(x); } while (!Q.empty()) Q.pop(); Q.push(1); memset (d, 0x3f, sizeof (d)); memset (mark, 0, sizeof (mark)); mark[1] = true ; d[1] = 0; while (!Q.empty()) { int h = Q.front(); Q.pop(); for ( int i = 0; i < G[h].size(); i ++) { int v = G[h][i], r = relax(h, v, W[h][i]); if (!mark[v] && r) { mark[v] = true ; Q.push(v); } } mark[h] = false ; } printf ( "%d\n" , d[t] == 0x3f3f3f3f? -1 : d[t]); } return 0; }

（3）map + cin :

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#include <stdio.h> #include <string.h> #include <iostream> #include <algorithm> #include <vector> #include <queue> #include <set> #include <map> #include <string> #include <math.h> #include <stdlib.h> #include <time.h> #include <map> using namespace std; const int maxn = 2e4 +7; map<string, int > mp; int n; vector<vector< int > >G, W; queue< int > Q; bool mark[maxn]; int d[maxn]; bool relax( int u, int v, int w) { if (d[v] > d[u] + w) { d[v] = d[u] + w; return true ; } return false ; } int main() { #ifndef ONLINE_JUDGE freopen ( "in.txt" , "r" , stdin); #endif // ONLINE_JUDGE string s1, s2, S; int x, m; while (cin >> m, ~m) { cin >> s1 >> s2; S = s2; n = 1; mp.clear(); G.clear(); W.clear(); G.resize(maxn + 2); W.resize(maxn + 2); if (!mp[s1]) mp[s1] = n ++; if (!mp[s2]) mp[s2] = n ++; for ( int i = 0; i < m; i ++) { cin >> s1 >> s2 >> x; if (!mp[s1]) mp[s1] = n ++; if (!mp[s2]) mp[s2] = n ++; G[mp[s1]].push_back(mp[s2]); G[mp[s2]].push_back(mp[s1]); W[mp[s1]].push_back(x); W[mp[s2]].push_back(x); } while (!Q.empty()) Q.pop(); Q.push(1); memset (d, 0x3f, sizeof (d)); memset (mark, 0, sizeof (mark)); mark[1] = true ; d[1] = 0; while (!Q.empty()) { int h = Q.front(); Q.pop(); for ( int i = 0; i < G[h].size(); i ++) { int v = G[h][i], r = relax(h, v, W[h][i]); if (!mark[v] && r) { mark[v] = true ; Q.push(v); } } mark[h] = false ; } printf ( "%d\n" , d[mp[S]] == 0x3f3f3f3f? -1 : d[mp[S]]); } return 0; }

（4）map + scanf:

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