代码随想录算法训练营第十四天 | 二叉树的递归遍历、二叉树的迭代遍历、二叉树的统一迭代

二叉树的递归遍历

二叉树的迭代遍历

二叉树的统一迭代

二叉树的递归遍历

var preorderTraversal = function(root) {
    const res = [];

    const traverse = (node) => {
        if (!node)  return;

        res.push(node.val);
        traverse(node.left);
        traverse(node.right);
    }

    traverse(root);
    return res;
};

二叉树的迭代遍历

var preorderTraversal = function(root) {
    if (!root)  return [];

    const res = [];
    const stk = [];
    stk.push(root);

    while(stk.length > 0) {
        const node = stk.pop();
        res.push(node.val);

        if (node.right) {
            stk.push(node.right);
        }
        if (node.left) {
            stk.push(node.left);
        }
    }
    return res;
};

var postorderTraversal = function(root) {
    if (!root)  return [];
    const res = [];
    const stk = [];
    stk.push(root);

    while(stk.length > 0) {
        const node = stk.pop();
        res.push(node.val);

        if (node.left) stk.push(node.left);
        if (node.right) stk.push(node.right);
    }
    return res.reverse();
};

var inorderTraversal = function(root) {
    if (!root)  return [];

    const res = [];
    const stk = [];
    let node = root;

    while (node || stk.length > 0) {
        if (node) {
            stk.push(node);
            node = node.left;
        } else {
            node = stk.pop();
            res.push(node.val);
            node = node.right;
        }
    }

    return res;
};

二叉树的统一迭代

• 感想：每次弹出当前节点 <=> 重新整理该节点下的子树顺序

var inorderTraversal = function(root) {
    if (!root)  return [];

    const res = [];
    const stk = [];
    
    let node = root;
    stk.push(node);
    while (stk.length > 0) {
        node = stk.pop();
        if (node) {
            if (node.right) stk.push(node.right);
            stk.push(node);
            stk.push(null);
            if (node.left)  stk.push(node.left);
        } else {
            node = stk.pop();
            res.push(node.val);
        }
    }

    return res;
};