Problem
Given a string s and a dictionary of words dict, determine if s can be break into a space-separated sequence of one or more dictionary words.
ExampleGiven s = "lintcode", dict = ["lint", "code"].
Return true because "lintcode" can be break as "lint code".
Note基础动规题目,有几个细节要注意。dp[0]是指,当s为空的时候的word-dict映射布尔值;另外,循环s第i个字符的时候,若该位已经判断过没有映射在dict中的word,就跳过;若这一位开始,加上从dict中取词的长度越界,则跳过;若dict中的取词和这一位起始的子字符串相等,则给子字符串的最后一个字符映射的dp[j]赋true。
Solutionpublic class Solution { public boolean wordBreak(String s, Setdict) { int n = s.length(); boolean[] dp = new boolean[n+1]; dp[0] = true; for (int i = 0; i < n; i++) { if (!dp[i]) continue; for (String word: dict) { int l = word.length(), j = i + l; if (j > n || dp[j]) continue; if (word.equals(s.substring(i, j))) dp[j] = true; } } return dp[n]; } }
Update 2018-9
class Solution { public boolean wordBreak(String s, ListwordDict) { Set dict = new HashSet<>(wordDict); int n = s.length(); boolean[] dp = new boolean[n+1]; dp[0] = true; for (int i = 1; i <= n; i++) { for (int j = 0; j < i; j++) { if (dp[j] && dict.contains(s.substring(j, i))) dp[i] = true; } } return dp[n]; } }
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