.\173.binary-search-tree-iterator ok

侯利朋 · 侯利朋 · commit c9767e3a8998 · 2019-08-30T19:53:42.000+08:00
diff --git a/173.binary-search-tree-iterator-1.go b/173.binary-search-tree-iterator-1.go
@@ -0,0 +1,54 @@
+/*
+ * @lc app=leetcode id=173 lang=golang
+ *
+ * [173] Binary Search Tree Iterator
+ */
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+//  44 ms, faster than 77.78%
+// 缓存所有节点
+type BSTIterator struct {
+	Buf   []int
+	Index int
+}
+
+func Constructor(root *TreeNode) BSTIterator {
+	// 中序遍历，缓存数据
+	rtn := BSTIterator{}
+	inOrder(root, &rtn.Buf)
+	rtn.Index = 0
+	return rtn
+}
+
+func inOrder(root *TreeNode, seq *[]int) {
+	if root == nil {
+		return
+	}
+	inOrder(root.Left, seq)
+	*seq = append(*seq, root.Val)
+	inOrder(root.Right, seq)
+}
+
+/** @return the next smallest number */
+func (this *BSTIterator) Next() int {
+	this.Index++
+	return this.Buf[this.Index-1]
+}
+
+/** @return whether we have a next smallest number */
+func (this *BSTIterator) HasNext() bool {
+	return this.Index < len(this.Buf)
+}
+
+/**
+ * Your BSTIterator object will be instantiated and called as such:
+ * obj := Constructor(root);
+ * param_1 := obj.Next();
+ * param_2 := obj.HasNext();
+ */
diff --git a/508.most-frequent-subtree-sum.go b/508.most-frequent-subtree-sum.go
@@ -14,11 +14,14 @@
 // 12 ms, faster than 68.85%
 // map缓存所有结果
 func findFrequentTreeSum(root *TreeNode) []int {
-	tmp := make(map[int]int)
-	sum(root, tmp)
+	if root == nil {
+		return []int{}
+	}
+	counter := make(map[int]int)
+	sum(root, counter)
 	maxTime := -1
 	rtn := []int{}
-	for k, v := range tmp {
+	for k, v := range counter {
 		if v > maxTime {
 			maxTime = v
 			rtn = append(rtn, k)
@@ -34,14 +37,7 @@ func sum(root *TreeNode, tmp map[int]int) int {
 	if root == nil {
 		return 0
 	}
-	l, r := 0, 0
-	if root.Left != nil {
-		l = sum(root.Left, tmp)
-	}
-	if root.Right != nil {
-		r = sum(root.Right, tmp)
-	}
-
-	tmp[l+r+root.Val]++ // 只在此处统计一次结果，在上面的left或right判断中不记录，否则会导致多计算一次
-	return l + r + root.Val
+	data := sum(root.Left, tmp) + sum(root.Right, tmp) + root.Val
+	tmp[data]++
+	return data
 }
