前端-二叉树的中序遍历

/*
 * @lc app=leetcode.cn id=94 lang=typescript
 *
 * [94] 二叉树的中序遍历
 */

// @lc code=start
/**
 * 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)
 *     }
 * }
 */

// 非递归的方式
function inorderTraversal(
  root: TreeNode | null,
  res: Array = []
): number[] {
  let p: any = root;
  const stack: Array = [];
  while (p || stack.length) {
    if (p) {
      stack.push(p);
      p = p.left;
    } else {
      p = stack.pop();
      res.push(p.val);
      p = p.right;
    }
  }
  return res;
}

function inorderTraversal2(
  root: TreeNode | null,
  res: Array = []
): number[] {
  if (!root) {
    return res;
  }
  inorderTraversal(root.left, res);
  res.push(root.val);
  inorderTraversal(root.right, res);
  return res;
}
// @lc code=end