1️⃣ 深度优先搜索

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;
// 对于二叉树来说，深度优先搜索和前序遍历的顺序是一样的。
function deepSearch(root, target) {
  if (root == null) return false;
  if (root.value == target) return true;
  var left = deepSearch(root.left, target);
  var right = deepSearch(root.right, target);
  return left || right;
}
console.log(deepSearch(a, 'i'));

1️⃣ 广度优先搜索

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(rootList, target) {
  if (rootList == null || rootList.length == 0) return false;
  var childList = []; // 当前层所有节点的子节点, 在下一次时就可以一层一层遍历
  for (let i = 0; i < rootList.length; i++) {
    if (rootList[i] != null && rootList[i].value == target) {
      return true;
    } else {
      childList.push(rootList[i].left);
      childList.push(rootList[i].right);
    }
  }
  console.log(childList);
  return fun(childList, target);
}
console.log(fun([a], 'i'));