add new solutions

solutions/2/q208/solution.go

@@ -0,0 +1,105 @@
+package q208
+
+type tNode struct {
+	str     string
+	childs  [26]*tNode
+	hasWord bool
+}
+
+func (n *tNode) index() int { return index(n.str) }
+
+func (n *tNode) split(prefixLen int) (*tNode, *tNode) {
+	if len(n.str) < prefixLen {
+		panic("cannot split node")
+	}
+	if len(n.str) == prefixLen {
+		return n, nil
+	}
+
+	prefix := n.str[:prefixLen]
+	n.str = n.str[prefixLen:]
+	p := &tNode{str: prefix}
+	p.childs[n.index()] = n
+	return p, n
+}
+
+func commonPrefix(a, b string) int {
+	minLen := min(len(a), len(b))
+	for i := range minLen {
+		if a[i] != b[i] {
+			return i
+		}
+	}
+	return minLen
+}
+
+func index(str string) int {
+	if len(str) > 0 {
+		return int(str[0] - 'a')
+	}
+	return -1 // root
+}
+
+type Trie struct {
+	root *tNode
+}
+
+func Constructor() Trie {
+	return Trie{
+		root: &tNode{},
+	}
+}
+
+func (t *Trie) Insert(word string) {
+	node := t.root
+	for len(word) > 0 {
+		idx := index(word)
+		next := node.childs[idx]
+		if next != nil {
+			pflen := commonPrefix(word, next.str)
+			next, _ = next.split(pflen)
+			node.childs[next.index()] = next
+			word = word[pflen:]
+		} else {
+			next = &tNode{str: word}
+			word = ""
+			node.childs[idx] = next
+		}
+		node = next
+	}
+	node.hasWord = true
+}
+
+func (t *Trie) Search(word string) bool {
+	node := t.root
+	for len(word) > 0 {
+		next := node.childs[index(word)]
+		if next == nil {
+			return false
+		}
+		pflen := commonPrefix(word, next.str)
+		if pflen != len(next.str) {
+			return false
+		}
+		word = word[pflen:]
+		node = next
+	}
+	return node.hasWord
+}
+
+func (t *Trie) StartsWith(prefix string) bool {
+	node := t.root
+	for len(prefix) > 0 {
+		next := node.childs[index(prefix)]
+		if next == nil {
+			return false
+		}
+		pflen := commonPrefix(prefix, next.str)
+		if pflen != len(next.str) && pflen != len(prefix) {
+			return false
+		}
+		prefix = prefix[pflen:]
+		node = next
+	}
+	return true
+}