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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"].
Dynamic Programming Backtracking
方法一：
DFS，
start已知，当start超过str长度时，说明全部字符串都能找到了。。
小数据可过，大数据时超时
class Solution { private: // DFS void wordBreak(string s, int start, unordered_set<string> & dict) { size_t size = s.size(); if(size == 0) return; if(start >= size) { string tmpStr; for(int i = 0; i < m_str.size(); i++) { if(i == m_str.size() - 1) tmpStr += m_str[i]; else tmpStr += m_str[i] + " "; } m_strs.push_back(tmpStr); } for( int i = start; i <size; i++) { string str = s.substr(start, i-start+1); if(dict.find(str) != dict.end()) { m_str.push_back(str); wordBreak(s,i+1, dict); m_str.pop_back(); } } } public: vector<string> wordBreak(string s, unordered_set<string>& wordDict) { m_str.clear(); m_strs.clear(); wordBreak(s,0, wordDict); return m_strs; } private: vector<string> m_str; vector<string> m_strs; };
方法二：
长度为 n 的字符串有 n+1 个隔板
基于dp之后，使用 vector<vector<string> > map 来保存当前的划分，
map[i] = {map[j]中原有的划分字符串} + s[j+1, i]，if s[j+1, i] 存在于字典中，
具例子，
s = "catsanddog",
dict = ["cat", "cats", "and", "sand", "dog"].
map[7] = {"cat sand", "cats and""}
map[10] = {"cat sand dog", "cats and dog"}, dog 在字典中。
但是 Status: Memory Limit Exceeded，头一次遇到这个错误。
vector<string> wordBreak2(string s, set<string> &dict) { vector<bool> f(s.size() + 1, false); vector<string> tmpStrVec; vector<vector<string> > map(s.size()+ 1, tmpStrVec); f[0] = true; for (int i = 1; i <= s.size(); ++i) { for (int j = i - 1; j >= 0; --j) { string subStr = s.substr(j, i-j); if (f[j] && dict.find(subStr) != dict.end()) { f[i] = true; vector<string> strVec = map[j]; if(strVec.size() == 0) { strVec.push_back(subStr); map[i] = strVec; } else { for(int k = 0; k < strVec.size(); k++) { strVec[k] += " " + subStr ; map[i].push_back(strVec[k]); } } } } } return map[s.size()];
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原文地址：http://www.cnblogs.com/diegodu/p/4560937.html
