[leetcode]139. Word Break

Given a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

For example, given
s = "leetcode",
dict = ["leet", "code"].

Return true because "leetcode" can be segmented as "leet code".

Subscribe to see which companies asked this question

分析：动态规划，v[i]表示第i个字母不包括这个之前能否被分词；对于比i小的任意一个j，如果j到i的单词在dict内，且v[j]为true，那么v[i]就可以判断为true。

代码：

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