LeetCode——(每日一题)恢复空格

直接dp

public int respace(String[] dictionary, String sentence) {
        int n = sentence.length();
        if(0==n)return 0;
        int[] dp = new int[n+1];
        for(int i = 1 ; i <= n ; i++)
        {
            dp[i] = dp[i-1] + 1;
            for(String word:dictionary)
            {
                if(word.length() <= i)
                {
                    if(sentence.substring(i-word.length(),i).equals(word))
                    {
                        dp[i] = Math.min(dp[i],dp[i-word.length()]);
                    }
                }
            }
        }
        return dp[n];
     }

dp+字典树(优化查找过程)

class Solution {
    public int respace(String[] dictionary, String sentence) {
        Trie root = new Trie();
        for(String word : dictionary)
        {
            root.insert(word);
        }
        int n = sentence.length();
        int[] dp = new int[n+1];
        for(int i = 1; i <= n ; i++)
        {
            dp[i] = dp[i-1] + 1;
            Trie cur = root;
            for(int j = i ; j>= 1 ; j--)
            {
                int t = sentence.charAt(j - 1) - 'a';
                if(null == cur.next[t])
                {
                    break;
                } 
                else if(cur.next[t].isEnd)
                {
                    dp[i] = Math.min(dp[i] , dp[j-1]);
                }
                cur = cur.next[t];
            }
        }
        return dp[n];
    }
}
class Trie{
    public Trie[] next;
    public boolean isEnd;
    public Trie()
    {
        next = new Trie[26];
        isEnd = false;
    }

    public void insert(String word)
    {
        Trie cur = this;
        int n = word.length();
        for( int i = n -1 ; i >= 0 ; i--)
        {
            int t = word.charAt(i)  -  'a';
            if(null == cur.next[t])
            {
                cur.next[t] = new Trie();
            }
            cur = cur.next[t];
        }
        cur.isEnd = true;
    }

}