用二叉树实现学生成绩的计数（随机产生100个学生成绩）

            function
             Node(data, left, right) {
        
            this.data = data;
        this.count = 1;
        this.left = left;
        this.right = right;
        this.show = show;
    }
    function show() {
        returnthis.data;
    }
    function BST() {
        this.root = null;
        this.insert = insert;
        this.find = find;
        this.insert = insert;
        this.update = update;
    }
    function insert(data) {
        var n = new Node(data, null, null);
        if (this.root == null) {
            this.root = n;
        } else {
            var current = this.root;
            var parent;
            while (true) {
                parent = current;
                if (data < current.data) {
                    current = current.left;
                    if (current == null) {
                        parent.left = n;
                        break;
                    }
                } else {
                    current = current.right;
                    if (current == null) {
                        parent.right = n;
                        break;
                    }
                }
            }
        }
    }
    function find(data) {
        var current = this.root;
        while (current != null) {
            if (current.data == data) {
                return current;
            } elseif (data < current.data) {
                current = current.left;
            } else {
                current = current.right;
            }
        }
        returnnull;
    }
    function update(data) {
        var grade = this.find(data);
        grade.count++;
        return grade;
    }
    function prArray(arr) {//每行十个元素显示数组中元素for ( var i = 0; i < arr.length; ++i) {
            document.write(arr[i] + " ");
            if ((i + 1) % 10 == 0) {
                document.write("<br /> ");
            }
        }
    }
    function genArray(length) {//产生指定元素个数的数组var arr = [];
        for ( var i = 0; i < length; ++i) {
            arr[i] = Math.floor(Math.random() * 101);
        }
        return arr;
    }
    var grades = genArray(100);
    prArray(grades);
    var gradedistro = new BST();
    for ( var i = 0; i < grades.length; ++i) {//将数组中元素添加到二叉树中var g = grades[i];
        var grade = gradedistro.find(g);
        if (grade == null) {
            gradedistro.insert(g);
        } else {
            gradedistro.update(g);
        }
    }

    document.write("*************** " + "<br />");
    var g = 45;
    var aGrade = gradedistro.find(g);
    if (aGrade == null) {
        document.write("No occurrences of " + g);
    } else {
        document.write("Occurrences of " + g + ": " + aGrade.count);
    }