Trie UVA 11732 "strcmp()" Anyone?

 

题目传送门

题意：询问所有字符串的比较次数和(注意for循环内的比较也算)

分析：将所有字符串插入到字典树上，然后结点信息记录有几个字符串，那么每走到一个结点就能知道比较到此时需要的次数。学习到链表存结点

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
const int N = 4e3 + 5;
const int M = 1e3 + 5;
const int NODE = N * M;
struct Trie	{
	int head[NODE], nex[NODE];
	char ch[NODE];
	int cnt[NODE];
	int sz;
	void clear()	{
		sz = 1;	cnt[0] = head[0] = nex[0] = 0;
	}
	void insert(char *str)	{
		int u = 0, len = strlen (str);
		cnt[0]++;
		for (int i=0; i<=len; ++i)	{
			bool found = false;
			int v;
			for (v=head[u]; v; v=nex[v])	{
				if (ch[v] == str[i])	{
					found = true;	break;
				}
			}
			if (!found)	{       //插入到链表的头结点后一个
				v = sz++;
				cnt[v] = 0;
				ch[v] = str[i];
				nex[v] = head[u];
				head[u] = v;
				head[v] = 0;
			}
			u = v;	cnt[u]++;
		}
	}
	void query(int u, int dep, ll &res)	{
		if (!head[u])	{
			res += cnt[u] * (cnt[u] - 1) * dep;
            return ;
		}
		int sum = 0, tmp = cnt[u];
		for (int v=head[u]; v; v=nex[v])	{
		    //sum += cnt[v] * (cnt[u] - cnt[v]);
            res += cnt[v] * (tmp - cnt[v]) * (dep * 2 + 1);
			tmp -= cnt[v];
        }
        //res += sum / 2 * (2 * dep + 1);
		for (int v=head[u]; v; v=nex[v])	{
			query (v, dep + 1, res);
		} 
	}
}trie;
char word[M];

int main(void)	{
	int n, cas = 0;
	while (scanf ("%d", &n) == 1)	{
		if (!n)	break;
		trie.clear ();
		for (int i=0; i<n; ++i)	{
			scanf ("%s", &word);
			trie.insert (word);
		}
		ll ans = 0;
		trie.query (0, 0, ans);
		printf ("Case %d: %lld\n", ++cas, ans);
	}

	return 0;
}