leetcode update

content/posts/leetcode.md

@@ -3528,3 +3528,86 @@ func addOneRow(root *TreeNode, val int, depth int) *TreeNode {
 ### 总结
 
 本题也可使用dfs结合变量记录当前深度来解决.
+
+## day50 2024-04-17
+
+### 988. Smallest String Starting From Leaf
+
+You are given the root of a binary tree where each node has a value in the range [0, 25] representing the letters 'a' to 'z'.
+
+Return the lexicographically smallest string that starts at a leaf of this tree and ends at the root.
+
+As a reminder, any shorter prefix of a string is lexicographically smaller.
+
+For example, "ab" is lexicographically smaller than "aba".
+
+A leaf of a node is a node that has no children.
+
+![0417XhbdaAO3QUHm](https://testingcf.jsdelivr.net/gh/game-loader/picbase@master/uPic/0417XhbdaAO3QUHm.png)
+
+### 题解
+
+使用递归实现dfs, 在dfs的过程中将路径上经过的节点数组作为参数传递给子节点, 对子节点执行dfs. dfs中将父路径的数组和左右两个子树返回的数组分别拼接, 对拼接后的数组进行比较, 将较小的作为返回值返回. 最终在根节点即可返回全局最小字典序字符串.
+
+### 代码
+
+```go
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func smallestFromLeaf(root *TreeNode) string {
+	result := dfs(root,[]int{})
+	var output []byte
+	for _, value := range result {
+		newbyte := []byte{byte('a' + value)}
+		output = append(newbyte, output...)
+	}
+	return string(output)
+}
+
+func dfs(root *TreeNode, parent []int) ([]int) {
+	localminstring := []int{root.Val}
+    parentstring := append(parent, root.Val)
+	if root.Left == nil && root.Right == nil {
+		return localminstring
+	} else if root.Left == nil && root.Right != nil {
+		localminstring = append(localminstring, dfs(root.Right, parentstring)...)
+		return localminstring
+	} else if root.Left != nil && root.Right == nil {
+		localminstring = append(localminstring, dfs(root.Left, parentstring)...)
+		return localminstring
+	} else {
+        leftstring := dfs(root.Left, parentstring)
+        rightstring := dfs(root.Right, parentstring)
+        v1 := make([]int,1)
+        v1 = append(v1, parentstring...)
+        v2 := make([]int,0)
+        v2 = append(v2, parentstring...)
+        v1 = append(v1,leftstring...)
+        v2 = append(v2,rightstring...)
+		length1 := len(v1) - 1
+		length2 := len(v2) - 1
+		for length1 >= 0 && length2 >= 0 {
+			if v1[length1] < v2[length2] {
+				return append(localminstring, leftstring...)
+			} else if v1[length1] > v2[length2] {
+				return append(localminstring, rightstring...)
+			}
+			length1--
+			length2--
+		}
+		if length1 > length2 {
+            return append(localminstring, rightstring...)
+		} else {
+			return append(localminstring, leftstring...)
+		}
+	}
+
+}
+
+```