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

 1 // 18.7 Given a list of words, find out the longest word made of other words in the list.
 2 #include <iostream>
 3 #include <string>
 4 #include <unordered_set>
 5 #include <vector>
 6 using namespace std;
 7 
 8 class Solution {
 9 public:
10     string longestBreakableWord(unordered_set<string> &dict) {
11         unordered_set<string>::const_iterator usit;
12         string res = "";
13         
14         for (usit = dict.begin(); usit != dict.end(); ++usit) {
15             if (wordBreak(*usit, dict) && usit->length() > res.length()) {
16                 res = *usit;
17             }
18         }
19         
20         return res;
21     }
22 private:
23     bool wordBreak(string s, unordered_set<string> &dict) {
24         int n;
25         int i, j;
26         string str;
27         vector<int> dp;
28         
29         n = (int)s.length();
30         if (n == 0 || dict.empty()) {
31             return false;
32         }
33         dp.resize(n);
34         for (i = 0; i < n; ++i) {
35             str = s.substr(0, i + 1);
36             if (dict.find(str) != dict.end()) {
37                 dp[i] = 1;
38             } else {
39                 for (j = 0; j < i; ++j) {
40                     if (dp[j] && dict.find(s.substr(j + 1, i - j)) != dict.end()) {
41                         dp[i] = 1;
42                         break;
43                     }
44                 }
45                 if (j == i) {
46                     dp[i] = 0;
47                 }
48             }
49         }
50         
51         i = dp[n - 1];
52         dp.clear();
53         return i == 1;
54     }
55 };
56 
57 int main()
58 {
59     unordered_set<string> dict;
60     string s;
61     Solution sol;
62     int i, n;
63     
64     while (cin >> n && n > 0) {
65         for (i = 0; i < n; ++i) {
66             cin >> s;
67             dict.insert(s);
68         }
69         
70         cout << sol.longestBreakableWord(dict) << endl;
71     }
72     
73     return 0;
74 }