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.

Note

• The same word in the dictionary may be reused multiple times in the segmentation.
• You may assume the dictionary does not contain duplicate words.

Example 1

Input: s = "leetcode", wordDict = ["leet", "code"]
Output: true
Explanation: Return true because "leetcode" can be segmented as "leet code".

Example 2

Input: s = "applepenapple", wordDict = ["apple", "pen"]
Output: true
Explanation: Return true because "applepenapple" can be segmented as "apple pen apple".
            Note that you are allowed to reuse a dictionary word.

Example 3

Input: s = "catsandog", wordDict = ["cats", "dog", "sand", "and", "cat"]
Output: false

Optimal Solution

Complexity

• Time: O(n2)
• Space: O(nm)

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