题目： 

 

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解析： 

 

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代码： 

public boolean wordBreak(String s, List<String> wordDict) {//优化⼀：将字典里面的单词放入哈希表，为后续找字串提高速度Set<String> hash = new HashSet<>(wordDict);int n = s.length();boolean[] dp = new boolean[n+1];dp[0] = true;s = " "+ s;//处理下标映射for(int i = 1; i <= n; i++)for(int j = i; j >= 1; j--){if(dp[j-1] && hash.contains(s.substring(j,i+1))){dp[i] = true;break;//优化二：找到一个拼接成功可以跳出}}return dp[n];}