编程基础：随机且不重复的算法

问题描述：有A到L的一组字母，需要每次都随机排序输出，并且不能有重复。

程序算法分析：

首先解决数组 0 到 10的随机且不重复的问题。

接下来把数组的值按下标索引去取这一组字母。

最后把结果输出出来。

代码如下：

var containerSet = function(count) {
        var tempArr = [];
        
        for (var i=0; i < count; i++){
                tempArr[i]=i;
        }
        tempArr.sort(function() {
                return 0.5 - Math.random(); 
        });
        return tempArr;
}
                        
var containers = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L'];
var l = containers.length;
var countSet = containerSet(l);
var resultSet = [];
while(l--) {
        resultSet.push(containers[countSet[l]]);
}

console.log(resultSet);

程序的精妙之处在：

tempArr.sort(function() {
        return 0.5 - Math.random(); 
});

这是利用了Array的sort(compareFunction)方法中的compareFunction参数。具体请参考：

If compareFunction is supplied, the array elements are sorted according to the return value of the compare function. If a and b are two elements being compared, then:

• If compareFunction(a, b) is less than 0, sort a to a lower index than b.
• If compareFunction(a, b) returns 0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements. Note: the ECMAscript standard does not guarantee this behaviour, and thus not all browsers (e.g. Mozilla versions dating back to at least 2003) respect this.
• If compareFunction(a, b) is greater than 0, sort b to a lower index than a.
• compareFunction(a, b) must always returns the same value when given a specific pair of elements a and b as its two arguments. If inconsistent results are returned then the sort order is undefined

来源于： https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/sort