[力扣c++实现] 139. 单词拆分

139. 单词拆分

给你一个字符串 s 和一个字符串列表 wordDict 作为字典。请你判断是否可以利用字典中出现的单词拼接出 s 。

注意：不要求字典中出现的单词全部都使用，并且字典中的单词可以重复使用。

示例 1：

输入: s = “leetcode”, wordDict = [“leet”, “code”]
输出: true
解释: 返回 true 因为 “leetcode” 可以由 “leet” 和 “code” 拼接成。
示例 2：

输入: s = “applepenapple”, wordDict = [“apple”, “pen”]
输出: true
解释: 返回 true 因为 “applepenapple” 可以由 “apple” “pen” “apple” 拼接成。
注意，你可以重复使用字典中的单词。
示例 3：

输入: s = “catsandog”, wordDict = [“cats”, “dog”, “sand”, “and”, “cat”]
输出: false

提示：

1 <= s.length <= 300
1 <= wordDict.length <= 1000
1 <= wordDict[i].length <= 20
s 和 wordDict[i] 仅有小写英文字母组成
wordDict 中的所有字符串 互不相同

1.c++

/*
*   date       2022-03-26
*   author     zhangyb
*   city       hangzhou
*/

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <map>
#include <unordered_set>

using namespace std;

class Solution {
public:

  //解法1：bruce force : timeout
  bool DFS(string subStr,const map<string,int>& wordCnt,const vector<string>& wordDict)
  {
    if (subStr.length() == 0)
    {
      return true;
    }

    for (auto word:wordDict)
    {
      if (subStr.length() < word.length())
      {
        continue;
      }
      string tmp = subStr.substr(0,word.length());
      if (wordCnt.count(tmp))
      {
        if (DFS(subStr.substr(tmp.length(),subStr.length() - tmp.length()),wordCnt,wordDict))
        {
          return true;
        }
      }
    }
    return false;
  }

  //解法2，递归+记忆数组
  bool check(string s, unordered_set<string>& wordSet,int start,vector<int>& memo)
  {
    std::cout << __FUNCTION__ <<":" << __LINE__<< std::endl;

    if (start >= s.size())
    {
      return true;
    }

    /*
      这里通过检查缓存来提前判断是否当前位置已经计算过了，而不需要再次计算以节省时间.
      这里就是将多次遍历变为一次，从而实现优化的目的。
    */
    if (memo[start] != -1)
    {
      return memo[start];
    }

    for (int i = start + 1;i <= s.size();++i)
    {
      string tmp = s.substr(start,i - start);
      std::cout << "[" << i << "]: " << tmp << std::endl;
      if (wordSet.count(s.substr(start,i - start)) && check(s,wordSet,i,memo))
      {
        return memo[start] = 1;
      }
    }

    return memo[start] = 0;
  }

  bool wordBreak(string s, vector<string>& wordDict) {
    /*
    vector<vector<int>> sPos;
    map<string,int> wordCnt;
    for (auto word:wordDict)
    {
      ++wordCnt[word];
    }

    //本来认为加上排序，将较长的字符串放前面，就能减小时间复杂度，但是还是放弃挣扎吧，这道题就是测试要求更高的记忆数组和动态规划，暴力的DFS就是不行的
    std::sort(wordDict.begin(),wordDict.end(),[](string &lrd,string &rwd)
    {
        return lrd.length() > rwd.length();
    });
    return DFS(s,wordCnt,wordDict);
    */
    unordered_set<string> wordSet(wordDict.begin(),wordDict.end());
    #if 0
    for (auto &s:wordSet)
    {
      std::cout << s << std::endl;
    }
    return false;
    #endif
    vector<int> memo(s.size(),-1);
    return check(s,wordSet,0,memo);
  }
};


int main()
{
  #if 0
  string s{"leetcode"};
  vector<string> wordDict = {"leet","code"};
  #endif
 
  #if 1
  string s{"fohhemkkaecojceoaejkkoedkofhmohkcjmkggcmnami"};
  vector<string> wordDict = {"kfomka","hecagbngambii","anobmnikj","c","nnkmfelneemfgcl","ah","bgomgohl","lcbjbg","ebjfoiddndih","hjknoamjbfhckb","eioldlijmmla","nbekmcnakif","fgahmihodolmhbi","gnjfe","hk","b","jbfgm","ecojceoaejkkoed","cemodhmbcmgl","j","gdcnjj","kolaijoicbc","liibjjcini","lmbenj","eklingemgdjncaa","m","hkh","fblb","fk","nnfkfanaga","eldjml","iejn","gbmjfdooeeko","jafogijka","ngnfggojmhclkjd","bfagnfclg","imkeobcdidiifbm","ogeo","gicjog","cjnibenelm","ogoloc","edciifkaff","kbeeg","nebn","jdd","aeojhclmdn","dilbhl","dkk","bgmck","ohgkefkadonafg","labem","fheoglj","gkcanacfjfhogjc","eglkcddd","lelelihakeh","hhjijfiodfi","enehbibnhfjd","gkm","ggj","ag","hhhjogk","lllicdhihn","goakjjnk","lhbn","fhheedadamlnedh","bin","cl","ggjljjjf","fdcdaobhlhgj","nijlf","i","gaemagobjfc","dg","g","jhlelodgeekj","hcimohlni","fdoiohikhacgb","k","doiaigclm","bdfaoncbhfkdbjd","f","jaikbciac","cjgadmfoodmba","molokllh","gfkngeebnggo","lahd","n","ehfngoc","lejfcee","kofhmoh","cgda","de","kljnicikjeh","edomdbibhif","jehdkgmmofihdi","hifcjkloebel","gcghgbemjege","kobhhefbbb","aaikgaolhllhlm","akg","kmmikgkhnn","dnamfhaf","mjhj","ifadcgmgjaa","acnjehgkflgkd","bjj","maihjn","ojakklhl","ign","jhd","kndkhbebgh","amljjfeahcdlfdg","fnboolobch","gcclgcoaojc","kfokbbkllmcd","fec","dljma","noa","cfjie","fohhemkka","bfaldajf","nbk","kmbnjoalnhki","ccieabbnlhbjmj","nmacelialookal","hdlefnbmgklo","bfbblofk","doohocnadd","klmed","e","hkkcmbljlojkghm","jjiadlgf","ogadjhambjikce","bglghjndlk","gackokkbhj","oofohdogb","leiolllnjj","edekdnibja","gjhglilocif","ccfnfjalchc","gl","ihee","cfgccdmecem","mdmcdgjelhgk","laboglchdhbk","ajmiim","cebhalkngloae","hgohednmkahdi","ddiecjnkmgbbei","ajaengmcdlbk","kgg","ndchkjdn","heklaamafiomea","ehg","imelcifnhkae","hcgadilb","elndjcodnhcc","nkjd","gjnfkogkjeobo","eolega","lm","jddfkfbbbhia","cddmfeckheeo","bfnmaalmjdb","fbcg","ko","mojfj","kk","bbljjnnikdhg","l","calbc","mkekn","ejlhdk","hkebdiebecf","emhelbbda","mlba","ckjmih","odfacclfl","lgfjjbgookmnoe","begnkogf","gakojeblk","bfflcmdko","cfdclljcg","ho","fo","acmi","oemknmffgcio","mlkhk","kfhkndmdojhidg","ckfcibmnikn","dgoecamdliaeeoa","ocealkbbec","kbmmihb","ncikad","hi","nccjbnldneijc","hgiccigeehmdl","dlfmjhmioa","kmff","gfhkd","okiamg","ekdbamm","fc","neg","cfmo","ccgahikbbl","khhoc","elbg","cbghbacjbfm","jkagbmfgemjfg","ijceidhhajmja","imibemhdg","ja","idkfd","ndogdkjjkf","fhic","ooajkki","fdnjhh","ba","jdlnidngkfffbmi","jddjfnnjoidcnm","kghljjikbacd","idllbbn","d","mgkajbnjedeiee","fbllleanknmoomb","lom","kofjmmjm","mcdlbglonin","gcnboanh","fggii","fdkbmic","bbiln","cdjcjhonjgiagkb","kooenbeoongcle","cecnlfbaanckdkj","fejlmog","fanekdneoaammb","maojbcegdamn","bcmanmjdeabdo","amloj","adgoej","jh","fhf","cogdljlgek","o","joeiajlioggj","oncal","lbgg","elainnbffk","hbdi","femcanllndoh","ke","hmib","nagfahhljh","ibifdlfeechcbal","knec","oegfcghlgalcnno","abiefmjldmln","mlfglgni","jkofhjeb","ifjbneblfldjel","nahhcimkjhjgb","cdgkbn","nnklfbeecgedie","gmllmjbodhgllc","hogollongjo","fmoinacebll","fkngbganmh","jgdblmhlmfij","fkkdjknahamcfb","aieakdokibj","hddlcdiailhd","iajhmg","jenocgo","embdib","dghbmljjogka","bahcggjgmlf","fb","jldkcfom","mfi","kdkke","odhbl","jin","kcjmkggcmnami","kofig","bid","ohnohi","fcbojdgoaoa","dj","ifkbmbod","dhdedohlghk","nmkeakohicfdjf","ahbifnnoaldgbj","egldeibiinoac","iehfhjjjmil","bmeimi","ombngooicknel","lfdkngobmik","ifjcjkfnmgjcnmi","fmf","aoeaa","an","ffgddcjblehhggo","hijfdcchdilcl","hacbaamkhblnkk","najefebghcbkjfl","hcnnlogjfmmjcma","njgcogemlnohl","ihejh","ej","ofn","ggcklj","omah","hg","obk","giig","cklna","lihaiollfnem","ionlnlhjckf","cfdlijnmgjoebl","dloehimen","acggkacahfhkdne","iecd","gn","odgbnalk","ahfhcd","dghlag","bchfe","dldblmnbifnmlo","cffhbijal","dbddifnojfibha","mhh","cjjol","fed","bhcnf","ciiibbedklnnk","ikniooicmm","ejf","ammeennkcdgbjco","jmhmd","cek","bjbhcmda","kfjmhbf","chjmmnea","ifccifn","naedmco","iohchafbega","kjejfhbco","anlhhhhg"};
  #endif 

  #if 0
  string s{"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab"};
  vector<string> wordDict = {"a","aa","aaa","aaaa","aaaaa","aaaaaa","aaaaaaa","aaaaaaaa","aaaaaaaaa","aaaaaaaaaa"};
  #endif 

  Solution slu;
  cout << slu.wordBreak(s,wordDict) << endl;
  return 0;
}

1.解题思路