[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"

.

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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
;
}
};