Create 671. 二叉树中第二小的节点.md

skypesky · web-flow · commit 97627c4605ea · 2022-02-23T20:37:53.000+08:00
diff --git a/671. 二叉树中第二小的节点.md b/671. 二叉树中第二小的节点.md
@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+function findSecondMinimumValue(root: TreeNode | null): number {
+    if (!root.left) {
+        return -1;
+    }
+    return dfs(root, root.val, -1);
+};
+
+function dfs(
+    root: TreeNode,
+    minValue: number,
+    result: number,
+): number {
+
+    if (root.val > minValue) {
+        result = Math.min(result !== -1 ? result : root.val, root.val);
+    }
+
+    root.left && (result = dfs(root.left, minValue, result));
+    root.right && (result = dfs(root.right, minValue, result));
+
+    return result;
+}
