面试题 17.13. 恢复空格

class Solution {
    public int respace(String[] dictionary, String sentence) {
        int n = sentence.length();
        if(n == 0) return 0;
        Trie t = new Trie();
        for(String s : dictionary) {
            t.insert(s);
        }
        char[] arr = sentence.toCharArray();
        int[] dp = new int[n+1];  // dp[i] 代表以i为起点，最少的未识别字符数
        for(int i = n - 1; i >= 0; i--) {
            dp[i] = t.getMin(i,arr,dp);
        }

        return dp[0];

    }
}
    // Trie
class Trie {
    private TrieNode root;
    public Trie() {
        root = new TrieNode(' ');
    }
    public void insert(String s) {
        char[] arr = s.toCharArray();
        TrieNode node = root;
        for(int i = 0; i < arr.length; i++) {
            char c = arr[i];
            if(node.sons[c-'a'] == null) node.sons[c-'a'] = new TrieNode(c);
            node = node.sons[c-'a'];
        }
        node.isWord = true;
    }
    public int getMin(int i, char[] arr, int[] dp) {
        int ans = dp[i+1] + 1; // 初始化
        TrieNode node = root;
        for(; i < arr.length; i++) { // 从当前点向前找，看看有多少个从i开始的可识别字符数 dp[i] = dp[i+可识别数]
            if(node.sons[arr[i] - 'a'] != null) {
                node = node.sons[arr[i] - 'a'];
                if(node.isWord) {
                    ans = Math.min(ans,dp[i+1]);
                }
            } else {
                break;
            }
        }
        return ans;
    }
}
class TrieNode {
    TrieNode[] sons;
    char c;
    boolean isWord;
    public TrieNode(char c) {
        this.c = c;
        sons = new TrieNode[26];
    }
}