leetcode非递归遍历二叉树

var inorderTraversal = function(root) {
    // 中序遍历
    const number= []
    const arr = []
    while(true){
        while(root){
            arr.push(root)
            root = root.left
        }
        if (!arr.length) {
            break
        }
        let temp = arr.pop()
        number.push(temp.val)
        root = temp.right
    }
    return number
};

前序和后序基本差不多，后序也是当作前序来做的。注意入栈顺序

var preorderTraversal = function(root) {
    let arr =[]
    let number=[]
    if (!root){
        return []
    }
    arr.push(root)
    while(arr.length){
        let temp = arr.pop()
        number.push(temp.val)
        
        if (temp.right){
            arr.push(temp.right)
        }

        if (temp.left){
            arr.push(temp.left)
        }
    }
    return number
};

var postorderTraversal = function(root) {
    let arr =[]
    let number=[]
    if (!root){
        return []
    }
    arr.push(root)
    while(arr.length){
        let temp = arr.pop()
        number.push(temp.val)
        if (temp.left){
            arr.push(temp.left)
        }
        if (temp.right){
            arr.push(temp.right)
        }

    }
    return number.reverse()
};