POJ-3630 Phone List

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本文介绍了一种用于检测电话号码列表是否一致性的算法。在给定的电话号码列表中，算法判断是否存在某个号码作为另一个号码的前缀，从而决定列表是否一致。通过输入电话号码数量和具体号码进行测试，并输出一致或不一致的结果。

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Phone List

Time Limit: 1000MS		Memory Limit: 65536K

Description

Given a list of phone numbers, determine if it is consistent in the sense that no number is the prefix of another. Let's say the phone catalogue listed these numbers:

Emergency 911
Alice 97 625 999
Bob 91 12 54 26

In this case, it's not possible to call Bob, because the central would direct your call to the emergency line as soon as you had dialled the first three digits of Bob's phone number. So this list would not be consistent.

Input

The first line of input gives a single integer, 1 ≤ t ≤ 40, the number of test cases. Each test case starts with n, the number of phone numbers, on a separate line, 1 ≤ n ≤ 10000. Then follows n lines with one unique phone number on each line. A phone number is a sequence of at most ten digits.

Output

For each test case, output "YES" if the list is consistent, or "NO" otherwise.

Sample Input

Sample Output

NO
YES

————————————————————耐心的分割线————————————————————

思路：这个……字典树找前缀是吧……参见POJ-1056 IMMEDIATE DECODABILITY。这个思路是一样的。样式不同而已。

代码如下：

#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <iostream>
#include <stack>
#include <queue>
#include <algorithm>
using namespace std;
struct TrieNode {
	TrieNode* next[10];
	bool word;
}node[100010];
char dic[10010][15];
int nxt, flag;

int cmp(const void* a, const void* b) {
	return strcmp((char*)a, (char*)b);
}

TrieNode *NewNode() {
	memset(&node[nxt], 0, sizeof(TrieNode));
	return &node[nxt++];
}

void Insert(TrieNode* rt, char* s) {
	int len = strlen(s);
	for(int i = 0; i < len; i++) {
		int c = s[i] - '0';
		if(!rt->next[c])	rt->next[c] = NewNode();
		rt = rt->next[c];
		if(rt->word) {//一旦插入过程中遇见前缀，重复了，break
			flag = 0;
			break;
		}
	}
	rt->word = true;
}

int main() {
	int cas;
	scanf("%d", &cas);
	while(cas--) {
		int m;
		scanf("%d", &m);
		nxt = 0; flag = 1;
		TrieNode* root = NewNode();//初始化字典树
		for(int i = 0; i < m; i++)
			scanf("%s", dic[i]);
		qsort(dic, m, sizeof(dic[0]), cmp);//先按字典序排个序,否则插入一个单词后再插入它的前缀，没反应。
		for(int i = 0; i < m; i++)
			Insert(root, dic[i]);
		printf("%s\n", flag ? "YES" : "NO");
	}
	return 0;
}