[LeetCode] Word Break II

最新推荐文章于 2019-06-19 09:56:51 发布

原创最新推荐文章于 2019-06-19 09:56:51 发布 · 331 阅读

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本文介绍了一种算法，该算法能够将一个字符串通过查找字典中的有效词汇进行拆分，并返回所有可能的句子组合。示例中使用了字符串“catsanddog”及字典[catcatsandsanddog]进行演示。

Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.

Return all such possible sentences.

For example, given
s = "catsanddog",
dict = ["cat", "cats", "and", "sand", "dog"].

A solution is ["cats and dog", "cat sand dog"].

class Solution {
public:
    vector<string> wordBreak(string s, unordered_set<string> &dict) {
        int len = s.size();
        vector<vector<bool>> flag(len, vector<bool>(len, false));
        for(int i = 0; i < len; i++)
        {
            for(int j = 0; j < len; j++)
            {
                if(dict.find(s.substr(i,j-i+1)) != dict.end())
                    flag[i][j] = true;
            }
        }
        vector<string> result;
        for(int i = len-1; i >= 0; i--)
        {
            if(flag[i][len-1])
            {
                string str = s.substr(i, len-i);
                back(flag, i-1, s, str, result);
            }
        }
        return result;
    }
    void back(vector<vector<bool>> &flag, const int &i, const string &s, string str, vector<string> &result)
    {
        if(i==-1)
        {
            result.push_back(str);
            return;
        }
        for(int j = 0; j <= i; j++)
        {
            if(flag[j][i])
            {
                string cur_str = s.substr(j, i-j+1) + " " + str;
                back(flag, j-1, s, cur_str, result);
            }
        }
    }
};