【数据结构与算法】中序遍历的非递归实现

回忆一下递归实现


/**
/*** 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) {var retArr = []if (!root) return retArrvar hlpFunc = (r) => {if(!r) return if (r.left) { helpFunc(r.left) }retArr.push(r.val)if (r.right) { hlepFunc(r.right) }}helpFunc(root)return retArr
}

用模拟栈来实现（方法一）（一二写法不一样，但是本质是一致）


var inorderTraversal = function(root) {var retArr = []if (!root) return retArrlet cur = rootlet stack = []while(stack.length !==0 || cur) {if (cur) {stack.push(cur)cur = cur.left} else {var tmp = stack.pop()retArr.push(temp.val)cur = temp.right}}return retArr}

用模拟栈来实现（方法二）（一二写法不一样，但是本质是一致）


var inorderTraversal = function(root) {var retArr = []if (!root) return retArrlet cur = rootlet stack = []while(stack.length !==0 || cur) {while(cur) {stack.push(cur)cur = cur.left}var tmp = stack.pop()retArr.push(tmp.val)cur = tmp.right}return retArr

用模拟栈来实现（方法三）（与方法一是逆向操作）

var inorderTraversal = function(root) { var retArr = []if (!root) return retArrlet stack = []let cur =rootwhile( stack.length !== 0 || cur ) {if (cur) {stack.push(cur)cur = cur.right} else {var tmp = stack.pop()retArr.push(tmp.val)cur = tmp.left}}return retArr.reverse()
}