方法：hash 二分
最优化问题转化为判定性问题。先预处理每个string的前缀hash，然后对于每组query，二分答案。当两个prefix 的hash value相同的时候，稳妥的方法是用O（prefix.length())的方法检查这两个prefix是否相同（1.430s)； 本题采用 bkdr hash，如果当hash value相同就认定两个prefix 相同，也通过了testcase（0.290s)。
code:
1 #include <cstdio> 2 #include <cstring> 3 #include <algorithm> 4 #include <iostream> 5 #include <string> 6 #include <vector> 7 #include <stack> 8 #include <bitset> 9 #include <cstdlib> 10 #include <cmath> 11 #include <set> 12 #include <list> 13 #include <deque> 14 #include <map> 15 #include <queue> 16 #include <fstream> 17 #include <cassert> 18 #include <unordered_map> 19 #include <unordered_set> 20 #include <cmath> 21 #include <sstream> 22 #include <time.h> 23 #include <complex> 24 #include <iomanip> 25 #define Max(a,b) ((a)>(b)?(a):(b)) 26 #define Min(a,b) ((a)<(b)?(a):(b)) 27 #define FOR(a,b,c) for (ll (a)=(b);(a)<(c);++(a)) 28 #define FORN(a,b,c) for (ll (a)=(b);(a)<=(c);++(a)) 29 #define DFOR(a,b,c) for (ll (a)=(b);(a)>=(c);--(a)) 30 #define FORSQ(a,b,c) for (ll (a)=(b);(a)*(a)<=(c);++(a)) 31 #define FORC(a,b,c) for (char (a)=(b);(a)<=(c);++(a)) 32 #define FOREACH(a,b) for (auto &(a) : (b)) 33 #define rep(i,n) FOR(i,0,n) 34 #define repn(i,n) FORN(i,1,n) 35 #define drep(i,n) DFOR(i,n-1,0) 36 #define drepn(i,n) DFOR(i,n,1) 37 #define MAX(a,b) a = Max(a,b) 38 #define MIN(a,b) a = Min(a,b) 39 #define SQR(x) ((LL)(x) * (x)) 40 #define Reset(a,b) memset(a,b,sizeof(a)) 41 #define fi first 42 #define se second 43 #define mp make_pair 44 #define pb push_back 45 #define all(v) v.begin(),v.end() 46 #define ALLA(arr,sz) arr,arr+sz 47 #define SIZE(v) (int)v.size() 48 #define SORT(v) sort(all(v)) 49 #define REVERSE(v) reverse(ALL(v)) 50 #define SORTA(arr,sz) sort(ALLA(arr,sz)) 51 #define REVERSEA(arr,sz) reverse(ALLA(arr,sz)) 52 #define PERMUTE next_permutation 53 #define TC(t) while(t--) 54 #define forever for(;;) 55 #define PINF 1000000000000 56 #define newline ' ' 57 58 #define test if(1)if(0)cerr 59 using namespace std; 60 using namespace std; 61 typedef vector<int> vi; 62 typedef vector<vi> vvi; 63 typedef pair<int,int> ii; 64 typedef pair<double,double> dd; 65 typedef pair<char,char> cc; 66 typedef vector<ii> vii; 67 typedef long long ll; 68 typedef unsigned long long ull; 69 typedef pair<ll, ll> l4; 70 const double pi = acos(-1.0); 71 72 const int maxn = 1e5; 73 string str[maxn]; 74 vector<ull> hashstr[maxn]; 75 int n, q; 76 77 bool valid(int a, int b, int mid) 78 { 79 --a, --b, --mid; 80 // to be safe, one should perform the substring test on the following line. 81 return (hashstr[a][mid] == hashstr[b][mid]);// && str[a].substr(0, mid+1)==str[b].substr(0,mid+1)); 82 } 83 int main() 84 { 85 ios::sync_with_stdio(false); 86 cin.tie(0); 87 int T; cin >> T; 88 repn(kase, T) 89 { 90 cin >> n; 91 rep(i, n) cin >> str[i]; 92 rep(i, n) 93 { 94 hashstr[i].clear(); 95 ull cur = 0, len = str[i].length(); 96 rep(j, len) 97 { 98 cur = 131*cur + (ull)str[i][j]; 99 hashstr[i].pb(cur); 100 } 101 } 102 cout << "Case " << kase << ": "; 103 cin >> q; 104 rep(i, q) 105 { 106 int x, y; cin >> x >> y; 107 int left = 1, right = min(str[x-1].length(), str[y-1].length()), mid, ans=0; 108 while (left <= right) 109 { 110 mid = (left+right)>>1; 111 if (valid(x,y,mid)) 112 { 113 ans = mid; 114 left = mid+1; 115 } 116 else 117 right = mid-1; 118 } 119 cout << ans << newline; 120 } 121 } 122 } 123 /* 124 125 2 126 5 127 daffodilpacm daffodiliupc distancevector distancefinder distinctsubsequence 4 128 1 2 129 1 5 130 3 4 131 4 5 132 2 133 acm 134 icpc 135 2 136 1 2 137 2 2 138 139 */