139. Word Break

Problem:

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words. You may assume the dictionary does not contain duplicate words.

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

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

Analysis:

State: dp[i] s前i个字符是否满足word break

Transition: dp[i] == true, 满足 dp[j] == true && wordDict.contains(s.substring(i, j))

举个例子:

leet code

       j = 4   i = 8

dp[j] 表示leet知否满足word break。 因为dp[]要比s多一位，dp[j] 对应的j指向的前一位。s.substring(4,8) == code.

Solution:

class Solution {
    public boolean wordBreak(String s, List<String> wordDict) {
        int len = s.length();
        boolean[] dp = new boolean[len + 1];
        dp[0] = true;
        for (int i = 1; i <= len; i++) {
            for (int j = 0; j <= i; j++) {
                if (dp[j] && wordDict.contains(s.substring(j, i)) {
                    dp[i] = true;
                    break;
                }
            }
        }
        return dp[len];
    }
}