js 代码 实现二叉树的前序， 中序， 后序遍历

// 二叉树的生成
function NodeTree(value){
    this.value = value;
    this.left = null;
    this.right = null;
}
let ta = new NodeTree('a');
let tb = new NodeTree('b');
let tc = new NodeTree('c');
let td = new NodeTree('d');
let te = new NodeTree('e');
let tf = new NodeTree('f');
let tg = new NodeTree('g');
ta.left = tb;
ta.right = tc;
tb.left = td;
tb.right = te;
tc.left = tf;
tc.right = tg;
// 形如上面的这个格式，ta被称为一颗二叉树。 满二叉树， 完全二叉树
// 二叉树的遍历，分为三种，前序遍历，中序遍历，后续遍历
/**
 * 二叉树的前序遍历
 * @param treeList
 * @returns {null}
 */
function treeFrontEach(treeList){
    if (!treeList || treeList.value === null) return null;
    console.log(treeList.value);
    treeFrontEach(treeList.left);
    treeFrontEach(treeList.right);
}
// treeFrontEach(ta); 输出的结果 a b d e c f g
/**
 * 中序遍历
 * @param treeList
 * @returns {null}
 */
function treeMiddleEach(treeList){
    if (!treeList || treeList.value === null) return null;
    treeMiddleEach(treeList.left);
    console.log(treeList.value);
    treeMiddleEach(treeList.right);
}
// treeMiddleEach(ta); 输出的结果 d b e a c f c g
/**
 * 后序遍历
 * @param treeList
 * @returns {null}
 */
function treeEndEach(treeList){
    if (!treeList || treeList.value === null) return null;
    treeEndEach(treeList.left);
    treeEndEach(treeList.right);
    console.log(treeList.value);
}
treeEndEach(ta); 输出结果 d e b f g c a