.\1028.recover-a-tree-from-preorder-traversal ok

侯利朋 · 侯利朋 · commit aba0fd530e74 · 2019-08-31T17:17:59.000+08:00
diff --git a/1028.recover-a-tree-from-preorder-traversal.go b/1028.recover-a-tree-from-preorder-traversal.go
@@ -0,0 +1,76 @@
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+// 12 ms, faster than 95.92%
+func recoverFromPreorder(S string) *TreeNode {
+	nodes := [][]int{} // [depth,val]
+	for i := 0; i < len(S); {
+		dep := 0
+		for i < len(S) && S[i] == '-' {
+			dep++
+			i++
+		}
+		node := []int{dep, 0}
+		l := i
+		for i < len(S) && S[i] != '-' {
+			i++
+		}
+		node[1], _ = strconv.Atoi(S[l:i])
+		nodes = append(nodes, node)
+	}
+	return pre(nodes)
+}
+
+//
+func pre(nodes [][]int) *TreeNode {
+	if len(nodes) == 0 {
+		return nil
+	}
+	if len(nodes) == 1 {
+		return &TreeNode{nodes[0][1], nil, nil}
+	}
+
+	root := &TreeNode{}
+	root.Val = nodes[0][1]
+	dep := nodes[0][0]
+
+	if nodes[1][0] == nodes[0][0]+1 {
+		// 找 dep+1 切分两块
+		i := 2
+		for ; i < len(nodes); i++ {
+			if nodes[i][0] == dep+1 {
+				break
+			}
+		}
+		if i == len(nodes) {
+			// 右子树为nil
+			root.Right = nil
+		} else {
+			root.Right = pre(nodes[i:])
+		}
+		root.Left = pre(nodes[1:i])
+	} else {
+		// 左子树为nil
+		root.Left = nil
+		// 找 dep+1 切分两块
+		i := 2
+		for ; i < len(nodes); i++ {
+			if nodes[i][0] == dep+1 {
+				break
+			}
+		}
+		if i == len(nodes) {
+			// 右子树为nil
+			root.Right = nil
+		} else {
+			root.Right = pre(nodes[i:])
+		}
+	}
+
+	return root
+}
