《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 == 0 || dict.empty()) {
            return false;
        }
        dp.resize(n);
        for (i = 0; i < n; ++i) {
            str = s.substr(0, i + 1);
            if (dict.find(str) != dict.end()) {
                dp[i] = 1;
            } else {
                for (j = 0; j < i; ++j) {
                    if (dp[j] && dict.find(s.substr(j + 1, i - j)) != dict.end()) {
                        dp[i] = 1;
                        break;
                    }
                }
                if (j == i) {
                    dp[i] = 0;
                }
            }
        }
        
        i = dp[n - 1];
        dp.clear();
        return i == 1;
    }
};

int main()
{
    unordered_set<string> dict;
    string s;
    Solution sol;
    int i, n;
    
    while (cin >> n && n > 0) {
        for (i = 0; i < n; ++i) {
            cin >> s;
            dict.insert(s);
        }
        
        cout << sol.longestBreakableWord(dict) << endl;
    }
    
    return 0;
}