算法篇：前缀树

1.最多 n个指向子结点的链接，其中每个链接对应字母表数据集中的一个字母，
本文中假定 n 为 26，小写拉丁字母的数量。
2.布尔字段，以指定节点是对应键的结尾还是只是键前缀

type Trie struct {
    IsEnd bool 
    Link [26]*Trie
}


/** Initialize your data structure here. */
func Constructor() Trie {
    root := Trie{}
    return  root
}

/** Inserts a word into the trie. */
func (this *Trie) Insert(word string)  {
    var node *Trie = this
    for _, w := range []byte(word) {
        if node.Link[w - byte('a')] == nil {
            n := Trie{}
            node.Link[w - byte('a')] = &n
        }
        node = node.Link[w - byte('a')]
    }
    node.IsEnd = true
    return
}


/** Returns if the word is in the trie. */
func (this *Trie) Search(word string) bool {
    var node *Trie = this 
    for _, w := range []byte(word) {
        if node.Link[w - byte('a')] == nil {
            node = nil
            break
        }
        node = node.Link[w - byte('a')]
    }
    return node != nil && node.IsEnd
}


/** Returns if there is any word in the trie that starts with the given prefix. */
func (this *Trie) StartsWith(prefix string) bool {
    var node *Trie = this 
    for _, w := range []byte(prefix) {
        if node.Link[w - byte('a')] == nil {
            node = nil
            break
        }
        node = node.Link[w - byte('a')]
    }
    return node != nil
}


/**
 * Your Trie object will be instantiated and called as such:
 * obj := Constructor();
 * obj.Insert(word);
 * param_2 := obj.Search(word);
 * param_3 := obj.StartsWith(prefix);
 */