【字符串】【Trie】lcp 题解

求$\sum_{0<i<n}\sum_{i<j≤n}lcp(si,sj)$
建立Trie树暴力跑一下，点上用组合数计算结果

#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <cmath>
#include <cctype>
#include <cstring>
#include <algorithm>
#include <map>
#ifndef WIN32
#define Auto "%lld"
#else
#define Auto "%I64d"
#endif
using namespace std;

typedef class TrieNode {
    public:
        map<int, TrieNode*> next;
        int val;
        int ends;

        TrieNode():val(0), ends(0) {
        }
}TrieNode;

#define lim 1000005
TrieNode pool[lim];
TrieNode* top = pool;

inline TrieNode* newnode() {
    return top++;
}

typedef class Trie {
    public:
        TrieNode* root;

        Trie():root(newnode()) {}

        inline void insert(char *str) {
            TrieNode* p = root;
            for(char *ch = str; *ch; ch++) {
                int c = *ch - 'a';
                p->val++;
                if(!p->next[c])
                    p->next[c] = newnode();
                p = p->next[c];
            }
            p->val++;
            p->ends++;
        }
}Trie;

long long res = 0;
typedef map<int, TrieNode*>::iterator mii;
void getRes(TrieNode*& node, int len) {
    for(mii i = node->next.begin(); i != node->next.end(); i++)
        for(mii j = i; j != node->next.end(); j++)
            if(j != i)
                res += i->second->val * 1LL * j->second->val * len;
    for(mii i = node->next.begin(); i != node->next.end(); i++)
            getRes(i->second, len + 1);
    if(node->ends)
        res += (node->val - node->ends) * 1LL * node->ends * len,
        res += node->ends * 1LL * (node->ends - 1) / 2 * len;
}

int n;
char buf[lim];
Trie trie;

inline void init() {
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)
        scanf("%s", buf), trie.insert(buf);
}

inline void solve() {
    getRes(trie.root, 0);
    printf(Auto, res);
}

int main() {
    init();
    solve();
    return 0;
}