1️⃣ 二叉树的前序遍历

function Node(value) {
  this.value = value;
  this.left = null;
  this.right = null;
}
var a = new Node("a")
var b = new Node("b")
var c = new Node("c")
var d = new Node("d")
var e = new Node("e")
var f = new Node("f")
var g = new Node("g")
var h = new Node("h")
var i = new Node("i")
var j = new Node("j")
var k = new Node("k")
a.left = b;
a.right = c;
b.left = d;
b.right = e;
c.left = f;
c.right = g;
d.left = h;
d.right = i;
g.left = j;
g.right = k;
function fun(root) {
  if (root == null || root.length == 0) return;
  console.log(root.value);
  fun(root.left);
  fun(root.right);
}
fun(a); // a b d h i e c f g j k

1️⃣ 二叉树的中序遍历

function Node(value) {
  this.value = value;
  this.left = null;
  this.right = null;
}
var a = new Node("a")
var b = new Node("b")
var c = new Node("c")
var d = new Node("d")
var e = new Node("e")
var f = new Node("f")
var g = new Node("g")
var h = new Node("h")
var i = new Node("i")
var j = new Node("j")
var k = new Node("k")
a.left = b;
a.right = c;
b.left = d;
b.right = e;
c.left = f;
c.right = g;
d.left = h;
d.right = i;
g.left = j;
g.right = k;
function fun(root) {
  if (root == null || root.length == 0) return;
  fun(root.left);
  console.log(root.value);
  fun(root.right);
}
fun(a); // h d i b e a f c j g k

1️⃣ 二叉树的后序遍历

function Node(value) {
  this.value = value;
  this.left = null;
  this.right = null;
}
var a = new Node("a")
var b = new Node("b")
var c = new Node("c")
var d = new Node("d")
var e = new Node("e")
var f = new Node("f")
var g = new Node("g")
var h = new Node("h")
var i = new Node("i")
var j = new Node("j")
var k = new Node("k")
a.left = b;
a.right = c;
b.left = d;
b.right = e;
c.left = f;
c.right = g;
d.left = h;
d.right = i;
g.left = j;
g.right = k;
function fun(root) {
  if (root == null || root.length == 0) return;
  fun(root.left);
  fun(root.right);
  console.log(root.value);
}
fun(a); // h i d e b f j k g c a

1️⃣ 根据前序中序还原二叉树

前序结果：a b d h i e c f g j k
中序结果：h d i b e a f c j g k

const qian = ['a', 'b', 'd', 'h', 'i', 'e', 'c', 'f', 'g', 'j', 'k'];
const zhong = ['h', 'd', 'i', 'b', 'e', 'a', 'f', 'c', 'j', 'g', 'k'];
const hou = ['h', 'i', 'd', 'e', 'b', 'f', 'j', 'k', 'g', 'c', 'a'];
function Node(value) {
  this.value = value;
  this.left = null;
  this.right = null;
}
function fun(qian, zhong) {
  if (qian == null || zhong == null || qian.length == 0 || zhong.length == 0)
    return null;
  var root = new Node(qian[0]);
  var index = zhong.indexOf(root.value); // 找到根节点在中序遍历中的位置
  var qianLeft = qian.slice(1, 1 + index); // 前序遍历的左子树
  var qianRight = qian.slice(1 + index, qian.length); // 前序遍历的右子树
  var zhongLeft = zhong.slice(0, index); //中序遍历的左子树
  var zhongRight = zhong.slice(index + 1, zhong.length); // 中序遍历的右子树
  root.left = fun(qianLeft, zhongLeft); // 根据左子树的前序和中序还原左子树并赋值给 root.left
  root.right = fun(qianRight, zhongRight); // 根据右子树的前序和中序还原右子树并赋值给 root.right
  return root;
}
var root = fun(qian, zhong);
console.log(root);

1️⃣ 根据中序后序还原二叉树

中序结果：h d i b e a f c j g k
后序结果： h i d e b f j k g c a