《Cracking the Coding Interview》——第18章：难题——题目7

2014-04-29 03:05

题目：给定一个词典，其中某些词可能能够通过词典里其他的词拼接而成。找出这样的组合词里最长的一个。

解法：Leetcode上有Word Break这道题，和这题基本思路一致。

代码：

 // 18.7 Given a list of words, find out the longest word made of other words in the list.
 #include <iostream>
 #include <string>
 #include <unordered_set>
 #include <vector>
 using namespace std;

 class Solution {
 public:
     string longestBreakableWord(unordered_set<string> &dict) {
         unordered_set<string>::const_iterator usit;
         string res = "";

         for (usit = dict.begin(); usit != dict.end(); ++usit) {
             if (wordBreak(*usit, dict) && usit->length() > res.length()) {
                 res = *usit;
             }
         }

         return res;
     }
 private:
     bool wordBreak(string s, unordered_set<string> &dict) {
         int n;
         int i, j;
         string str;
         vector<int> dp;

         n = (int)s.length();
         if (n ==  || dict.empty()) {
             return false;
         }
         dp.resize(n);
         for (i = ; i < n; ++i) {
             str = s.substr(, i + );
             if (dict.find(str) != dict.end()) {
                 dp[i] = ;
             } else {
                 for (j = ; j < i; ++j) {
                     if (dp[j] && dict.find(s.substr(j + , i - j)) != dict.end()) {
                         dp[i] = ;
                         break;
                     }
                 }
                 if (j == i) {
                     dp[i] = ;
                 }
             }
         }

         i = dp[n - ];
         dp.clear();
         return i == ;
     }
 };

 int main()
 {
     unordered_set<string> dict;
     string s;
     Solution sol;
     int i, n;

     while (cin >> n && n > ) {
         for (i = ; i < n; ++i) {
             cin >> s;
             dict.insert(s);
         }

         cout << sol.longestBreakableWord(dict) << endl;
     }

     return ;
 }