LeetCode题解——wordBreak2

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"].

DPsolution 0ms:

class Solution {
public:
    vector<string> wordBreak(string s, unordered_set<string>& wordDict) {
        vector<string> res;
        int n = s.size();
        if(!n || wordDict.empty()) return res;
        
        int longestWord = 0;
        for(auto w:wordDict){
            longestWord = max(longestWord, int(w.size()));
        }
        
        
        vector<bool> D(n+1,false);
        D[0]= true;
        
        for(int i=n-1; i>=0; i--){
            if(wordDict.find(s.substr(i))!=wordDict.end()) break;
            if(i==0) return res;
        }
        
        vector<vector<string>> index(n+1,vector<string>());
        
        for(int i=1; i<=n; i++){
            for(int j=i-1; j>=max(0,i-longestWord); j--){
                if(D[j]){
                    string t = s.substr(j,i-j);
                    if(wordDict.find(t)!=wordDict.end()){
                        D[i] = true;
                        if(j==0){
                            index[i].push_back(t);
                        }
                        else 
                            for(auto w:index[j]){
                                index[i].push_back(w+' '+t);
                            }
                    }
                }
            }
        }
        
        return index[n];
    }
};

backtracking: oms

class Solution {
public:
    vector<string> wordBreak(string s, unordered_set<string>& wordDict) {
        vector<string> res;
        int n = s.size();
        if(!n || wordDict.empty()) return res;
        
        int longestWord = 0;
        for(auto w:wordDict){
            longestWord = max(longestWord, int(w.size()));
        }
        
        
        vector<bool> D(n+1,false);
        D[0]= true;
        
        for(int i=1; i<=n; i++){
            for(int j=i-1; j>=max(0,i-longestWord); j--){
                if(D[j]){
                    string t = s.substr(j,i-j);
                    if(wordDict.find(t)!=wordDict.end()){
                        D[i] = true;
                        break;
                    }
                }
            }
        }
        
        if(!D[n]) return res;
        
        string temp;
        getres(s,temp,res,D,wordDict,n);
        return res;
    }
    
    void getres(string s, string temp, vector<string>& res, vector<bool>& D,unordered_set<string>& wordDict,int end){
        if(end==0){
            res.push_back(temp.substr(0,temp.size()-1));
            return;
        }
        for(int i=end-1; i>=0; i--){
            if(D[i]){
               string t = s.substr(i,end-i);
               if(wordDict.find(t)!=wordDict.end()){
				    string temp1 = temp;
                    temp = t + ' ' + temp;
                    getres(s,temp,res,D,wordDict,i);
					temp = temp1;
               }
            }
        }
    }
};