LeetCode14. Longest Common Prefix(字典树：最长公共前缀)

题目链接：https://leetcode.com/problems/longest-common-prefix/

Write a function to find the longest common prefix string amongst an array of strings.（最长公共前缀）

解题思路：字典树。以任一串去查找，找到最长的且匹配数为n的即可，水题。

struct Trie{
    Trie *next[26];
    int cnt;
    //string str;
}*root;

int n;

string ans;

void insert(string s){
    Trie *p = root,*pnew;
    for(int i = 0;i < s.size();++ i){
        int x = s[i] - 'a';
        if(p->next[x] == NULL){
          pnew = new Trie;
          pnew->cnt = 1;
          for(int j = 0;j < 26;++ j){
              pnew->next[j] = NULL;
          }
          p->next[x] = pnew;
        }
        else p->next[x]->cnt++;
        p=p->next[x];
    }
}


int search(string s){
    Trie *p = root;
    bool f = 0;
    for(int i = 0;i < s.size();++ i){
        int x = s[i] - 'a';
        if(p->next[x] == NULL) return 0;
        if(p->next[x]->cnt == n){
            ans = s.substr(0,i+1);
            f = 1;
        }
        p = p->next[x];
    }
    return f;
}

void init(){
    root = new Trie;
    root->cnt = 0;
    for(int i = 0;i < 26;++ i){
        root->next[i] = NULL;
    }
}

class Solution {
public:
    string longestCommonPrefix(vector& strs) {
      n = strs.size();
      if(!n) return ans = "";
      init();
      for(int i = 0;i < n;++ i){
          insert(strs[i]);
      }
      if(!search(strs[0])) return ans = "";
      return ans;
    }
};