/*
     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’);

    a.left = c;
    a.right = b;
    c.left = f;
    c.right = g;
    b.left = d;
    b.right = e;

    function f1(root) {
    if (root == null) return;
    f1(root.left);
    console.log(root.value);
    f1(root.right);
    }

    f1(a);