poj 2001 Shortest Prefixes

trie樹

題意:
尋找到最短能區分出每一個字符串的前綴

Shortest Prefixes Time Limit: 1000MS Memory Limit: 30000K Total Submissions: 11976 Accepted: 5099 Description A prefix of a string is a substring starting at the beginning of the given string. The prefixes of "carbon" are: "c", "ca", "car", "carb", "carbo", and "carbon". Note that the empty string is not considered a prefix in this problem, but every non-empty string is considered to be a prefix of itself. In everyday language, we tend to abbreviate words by prefixes. For example, "carbohydrate" is commonly abbreviated by "carb". In this problem, given a set of words, you will find for each word the shortest prefix that uniquely identifies the word it represents.  In the sample input below, "carbohydrate" can be abbreviated to "carboh", but it cannot be abbreviated to "carbo" (or anything shorter) because there are other words in the list that begin with "carbo".  An exact match will override a prefix match. For example, the prefix "car" matches the given word "car" exactly. Therefore, it is understood without ambiguity that "car" is an abbreviation for "car" , not for "carriage" or any of the other words in the list that begins with "car".  Input The input contains at least two, but no more than 1000 lines. Each line contains one word consisting of 1 to 20 lower case letters. Output The output contains the same number of lines as the input. Each line of the output contains the word from the corresponding line of the input, followed by one blank space, and the shortest prefix that uniquely (without ambiguity) identifies this word. Sample Input carbohydrate cart carburetor caramel caribou carbonic cartilage carbon carriage carton car carbonate Sample Output carbohydrate carboh cart cart carburetor carbu caramel cara caribou cari carbonic carboni cartilage carti carbon carbon carriage carr carton carto car car carbonate carbona Source Rocky Mountain 2004

[Submit]   [Go Back]   [Status]   [Discuss]

#include <cstdio>
#include <cstdlib>
#include <string>
#include <cstring>
#include <algorithm>
#define maxn 1005
#define maxl 22

class node
{
public:
	int times;
	node* np[26];
	node()
	{
		times = 0;/*當前點被訪問次數*/
		for (int i = 0; i < 26; ++i)
			np[i] = NULL;
	}
};

node *root = new node;
node * cur = NULL, *new_node = NULL;

int str_num = 0;/*字符串數*/
char str[maxn][maxl];

void insert_str(char* a)/*插入一個字符串*/
{
	int len = strlen(a);
	int i = 0;

	cur = root;

	while (i < len)
	{
		char ch_tmp = a[i];
		int delta = ch_tmp - 'a';
		node* np_tmp = cur -> np[delta];/*對應字母對應的兒子指針*/
		if (np_tmp != NULL)
		{
			cur = np_tmp;
			++(cur -> times);/*兒子的次數加1*/
		}
		else/*新建結點*/
		{
			new_node = new node;
			++(new_node -> times);
			cur -> np[delta] = new_node;
			cur = new_node;
		}
		++i;
	}
}

void find_pre(char * a)/*查找最短前綴*/
{
	int len = strlen(a);
	int i = 0;
	cur = root;
	while (i < len)
	{
		char ch_tmp = a[i];
		int delta = ch_tmp - 'a';
		cur = cur -> np[delta];
		if (cur -> times == 1)
		{
			printf("%s ", a);
			a[i + 1] = '\0';
			printf("%s\n", a);
			return;
		}
		++i;
	}
	printf("%s %s\n", a, a);
	return;
}

int main()
{
	while (scanf("%s", str[str_num]) != EOF)
	{
		insert_str(str[str_num]);
		++str_num;
	}
	for (int i = 0; i < str_num; ++i)
	{
		find_pre(str[i]);
	}
	return 0;
}