經典遞歸

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"].

#include <iostream>
#include<map>
#include<vector>
#include<unordered_map>
#include<unordered_set>
#include<string>
using namespace std;


vector<string> combine(string s,vector<string> prev)
{
    for(int i = 0; i < prev.size(); ++ i)
    {
        prev[i] += " " + s;
    }
    return prev;
}
vector<string> wordBreak(string s, unordered_set<string>& wordDict)
{
    vector<string> res;
    if(wordDict.count(s))
    {
        res.push_back(s);
    }
    for(int i = 1; i < s.size(); ++ i)
    {
        string back = s.substr(i);
        if(wordDict.count(back))
        {
            string prev = s.substr(0,i);
            vector<string> pre = combine(back,wordBreak(prev,wordDict));
            res.insert(res.end(),pre.begin(),pre.end());
        }
    }
    return res;
}

int main()
{
    //dict =["cat", "cats", "and", "sand", "dog"].
    cout << "Hello world!" << endl;
    string s="catsanddog";
    unordered_set<string>A;
    A.insert("cat");
    A.insert("cats");
    A.insert("and");
    A.insert("sand");
    A.insert("dog");
    wordBreak(s,A);
    return 0;
}