Word Break

题目

Word Break

Given a string s and a dictionary of words dict, determine if s can be segmented into a spaceseparatedsequence of one or more dictionary words.For example, given s = "leetcode", dict = ["leet", "code"].Return true because "leetcode" can be segmented as "leet code".

分析

意思是给出一本词典以及一个字符串，能否切分这个字符串使得每个字串都在字典里面存在。
假设dp(i)表示长度为i的字串能否别切分，dp方程如下:

dp(i) = dp(j) && s[j, i) in dict, 0

解答

class Solution {public:    bool wordBreak(string s, unordered_set<string> &dict)     {        int len = (int)s.size();        vector<bool> dp(len + 1, false);        dp[0] = true;        for(int i = 1; i <= len; i++)         {            for(int j = i - 1; j >= 0; j--)             {                if(dp[j] && dict.find(s.substr(j, i - j)) != dict.end())                 {                    dp[i] = true;                    break;                }            }        }        return dp[len];    }};