LeetCode:word-breakII

题目描述

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"].

C/C++ (clang++ 3.3)

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class Solution {

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public:

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    //动态规划思想，记录子问题结果。。。。

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    unordered_map<string,vector<string>> hash;//加快执行速度。。。递归有使用，需外部声明

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    vector<string> wordBreak(string s, unordered_set<string> &dict) {

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        if(hash.find(s)!=hash.end())

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            return hash[s];

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        vector<string> res;

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        if(s.size()==0)

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            return res;

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        if(dict.find(s)!=dict.end())

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            res.push_back(s);//

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        for(int i=0;i<s.size();i++){

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            string pre=s.substr(0,i+1);

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            if(dict.find(pre)==dict.end())

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                continue;

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            string post=s.substr(i+1);

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            vector<string> tmp=wordBreak(post,dict);

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            for(int j=0;j<tmp.size();j++){

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                res.push_back(pre+" "+tmp[j]);

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            }

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        }

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        hash[s] = res;

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        return res;

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    }

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};