字典树_HDU1671

题目链接：Phone List
思路：字典树模板题。不需要用到Search函数，用全局变量flag标记结果输出YES还是NO。当一个字符串在参与建Trie树时，走过的路上的点有isStr标记为true就证明此前参与建Trie树的一个字符串是当前串的前缀；还有当前参与建Trie树的串，最后一个字符所在的节点，它有子节点证明当前串是某串前缀。分别处理一下两种情况：如样例中，先输入911，后输入91 12 54 26 与先输入 91 12 54 26 后输入 911 处理方式不同。详见代码：

#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>#include<queue>#include<stack>#include<vector>#include<cmath>#include<map>#include<set>#include<cstdlib>#define mem(a,b) memset(a,b,sizeof(a))#define INF 0x7ffffffftypedef long long ll;using namespace std;const int maxn = 1e4+10;const int MAX = 10;struct Trie{    bool isStr;    Trie *next[MAX];};bool flag;void BuildTrie(Trie *root, const char *s){    if(root == NULL || *s == '\0'){        return;    }    int i;    Trie *p = root;    while(*s != '\0'){        if(p -> next[*s - '0'] == NULL){            Trie *tmp = (Trie *)malloc(sizeof(Trie));            for(int i = 0; i < MAX; i++){                tmp -> next[i] = NULL;            }            tmp -> isStr = false;            p -> next[*s - '0'] = tmp;            p = p -> next[*s - '0'];        }else if(p -> next[*s - '0'] != NULL){            p = p -> next[*s - '0'];            if(*(s+1) == '\0'){                flag = false;                return;            }            if(p -> isStr == true){                flag = false;                return;            }        }        s++;    }    p -> isStr = true;}void dele(Trie *root){    int i;    for(int i = 0; i < MAX; i++){        if(root -> next[i] != NULL){            dele(root -> next[i]);        }    }    free(root);}//int Search(Trie *root,const char *s){//    Trie *p = root;//    while(p != NULL && *s != '\0'){//        p = p -> next[*s - 'a'];//        s++;//    }//    return (p != NULL && p -> isStr == true);//}int main(){    int T,i;    scanf("%d",&T);    while(T--){        int n;        char s[maxn];        Trie *root = (Trie *)malloc(sizeof(Trie));        for(int i = 0 ;i < MAX; i++){            root -> next[i] = NULL;        }        root -> isStr = false;        flag = true;        scanf("%d",&n);        getchar();        for(int i = 0; i < n; i++){            scanf("%s",s);            if(flag)            BuildTrie(root,s);        }        if(flag) puts("YES");        else puts("NO");        dele(root);    }    return 0;}