js 函数练习

1. 不借助临时变量，进行两个整数的交换

function swap(a,b){
  b = b - a;
  a = a + b;
  b = a - b;
  return [a, b];
}

原理：a = a + (b - a)

2. 找出下列正数组中的最大差值：[10, 5, 11, 4, 9]

function getMaxProfit(arr){
  var minValue = maxValue = arr[0];
  var maxProfit = 0;
  for(var i = 0; i < arr.length; i++){
    var currentValue = arr[i];
    minValue = Math.min(minValue, currentValue);
    maxValue = Math.max(maxValue, currentValue);
  }
  maxProfit = maxValue - minValue;
  return maxProfit;
}

3. 随机生成指定长度的字符串

function randomString(n){
  var str = get26Letters();
  var tmp = '', i = 0 ;
  for(i = 0; i < n; i++){
    tmp += str.charAt(Math.floor(Math.random() * str.length));
  }
  return tmp;
}

function get26Letters(){
  var str = '';
  for(var i = 0; i < 26; i++){
    str += String.fromCharCode(97+i);
  }
  return str;
}

4. 实现类似 getElementsByClassName 的功能

/*   function queryClassName(node, name){
    var starts = '(^|[\n\r\t\f])', ends = '([\n\r\t\f]|$)';
    var array = [], regex = new RegExp(starts + name + ends),
    elements = node.getElementsByTagName('*'),
    length = elements.length, i = 0 , element;
    while( i < length ){
        element = elements[i];
        if(regex.test(element.className)){
            array.push(element);
        }
        i += 1;
    }
    return array;
  }
*/