二叉树的迭代遍历

接 [二叉树的递归遍历] 文章

144. 二叉树的前序遍历

/**
 * 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 preorderTraversal = function(root, res = []) {
    if (!root) return res;
    const stack = [root];
    let cur = null;
    while (stack.length) {
        cur = stack.pop();
        res.push(cur.val);
        cur.right && stack.push(cur.right);
        cur.left && stack.push(cur.left);
    }
    return res;
}

94. 二叉树的中序遍历

/**
 * 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, res = []) {
    const stack = [];
    let cur = root;
    while (stack.length || cur) {
        if (cur) {
            stack.push(cur);
            // 左
            cur = cur.left;
        } else {
            // --> 弹出 中
            cur = stack.pop();
            res.push(cur.val);
            // 右
            cur = cur.right;
        }
    };
    return res;
};

145. 二叉树的后序遍历

/**
 * 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 postorderTraversal = function(root, res = []) {
    if (!root) return res;
    const stack = [root];
    let cur = null;
    do {
        cur = stack.pop();
        res.push(cur.val);
        cur.left && stack.push(cur.left);
        cur.right && stack.push(cur.right);
    } while (stack.length);
    return res.reverse();
};