规范格式

leetcode/0173.Binary-Search-Tree-Iterator/173. Binary Search Tree Iterator.go

@@ -0,0 +1,87 @@
+package leetcode
+
+import "container/heap"
+
+import (
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+// TreeNode define
+type TreeNode = structures.TreeNode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+// BSTIterator define
+type BSTIterator struct {
+	pq    PriorityQueueOfInt
+	count int
+}
+
+// Constructor173 define
+func Constructor173(root *TreeNode) BSTIterator {
+	result, pq := []int{}, PriorityQueueOfInt{}
+	postorder(root, &result)
+	for _, v := range result {
+		heap.Push(&pq, v)
+	}
+	bs := BSTIterator{pq: pq, count: len(result)}
+	return bs
+}
+
+func postorder(root *TreeNode, output *[]int) {
+	if root != nil {
+		postorder(root.Left, output)
+		postorder(root.Right, output)
+		*output = append(*output, root.Val)
+	}
+}
+
+/** @return the next smallest number */
+func (this *BSTIterator) Next() int {
+	this.count--
+	return heap.Pop(&this.pq).(int)
+}
+
+/** @return whether we have a next smallest number */
+func (this *BSTIterator) HasNext() bool {
+	return this.count != 0
+}
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * obj := Constructor(root);
+ * param_1 := obj.Next();
+ * param_2 := obj.HasNext();
+ */
+type PriorityQueueOfInt []int
+
+func (pq PriorityQueueOfInt) Len() int {
+	return len(pq)
+}
+
+func (pq PriorityQueueOfInt) Less(i, j int) bool {
+	return pq[i] < pq[j]
+}
+
+func (pq PriorityQueueOfInt) Swap(i, j int) {
+	pq[i], pq[j] = pq[j], pq[i]
+}
+
+func (pq *PriorityQueueOfInt) Push(x interface{}) {
+	item := x.(int)
+	*pq = append(*pq, item)
+}
+
+func (pq *PriorityQueueOfInt) Pop() interface{} {
+	n := len(*pq)
+	item := (*pq)[n-1]
+	*pq = (*pq)[:n-1]
+	return item
+}

leetcode/0173.Binary-Search-Tree-Iterator/173. Binary Search Tree Iterator_test.go

@@ -0,0 +1,29 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/halfrost/LeetCode-Go/structures"
+)
+
+func Test_Problem173(t *testing.T) {
+
+	root := structures.Ints2TreeNode([]int{9, 7, 15, 3, structures.NULL, structures.NULL, 20})
+	obj := Constructor173(root)
+	fmt.Printf("obj = %v\n", obj)
+	param1 := obj.Next()
+	fmt.Printf("param_1 = %v\n", param1)
+	param2 := obj.HasNext()
+	fmt.Printf("param_2 = %v\n", param2)
+	param1 = obj.Next()
+	fmt.Printf("param_1 = %v\n", param1)
+	param1 = obj.Next()
+	fmt.Printf("param_1 = %v\n", param1)
+	param1 = obj.Next()
+	fmt.Printf("param_1 = %v\n", param1)
+	param1 = obj.Next()
+	fmt.Printf("param_1 = %v\n", param1)
+	param2 = obj.HasNext()
+	fmt.Printf("param_2 = %v\n", param2)
+}

leetcode/0173.Binary-Search-Tree-Iterator/README.md

@@ -0,0 +1,38 @@
+# [173. Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/)
+
+
+## 题目
+
+Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.
+
+Calling `next()` will return the next smallest number in the BST.
+
+**Example:**
+
+![](https://assets.leetcode.com/uploads/2018/12/25/bst-tree.png)
+
+    BSTIterator iterator = new BSTIterator(root);
+    iterator.next();    // return 3
+    iterator.next();    // return 7
+    iterator.hasNext(); // return true
+    iterator.next();    // return 9
+    iterator.hasNext(); // return true
+    iterator.next();    // return 15
+    iterator.hasNext(); // return true
+    iterator.next();    // return 20
+    iterator.hasNext(); // return false
+
+**Note:**
+
+- `next()` and `hasNext()` should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
+- You may assume that `next()` call will always be valid, that is, there will be at least a next smallest number in the BST when `next()` is called.
+
+
+## 题目大意
+
+实现一个二叉搜索树迭代器。你将使用二叉搜索树的根节点初始化迭代器。调用 next() 将返回二叉搜索树中的下一个最小的数。
+
+## 解题思路
+
+- 用优先队列解决即可
+