# day17-二叉树的中序遍历

给定一个二叉树的根节点 root ,返回 它的 中序 遍历

示例 1:

输入:root = [1,null,2,3]
输出:[1,3,2]
1
2

示例 2:

输入:root = []
输出:[]
1
2

示例 3:

输入:root = [1]
输出:[1]
1
2

提示:

  • 树中节点数目在范围 [0, 100]
  • -100 <= Node.val <= 100
# 解法BFS
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var inorderTraversal = function(root) {
    if(!root) return []
    let res = [];
    let stack = [];
    let cur = root;
    while(stack.length || cur){
        // 找到最左侧那个子节点
        while(cur){
            stack.push(cur);
            cur = cur.left;
        }
        cur = stack.pop();
        res.push(cur.val);
        cur = cur.right;
    }
    return res
};
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