随机抽取不重复的数组元素

测试代码：

var arr0 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

var ranNum0 = 5;

console.log(getDiffArr(arr0, ranNum0));

 

方法实现：

1.  不断缩减原数组，一次抽一个

        function getDiffArr(arr, num) {
            var arrOut = [];
            for (var i = 0; i < num; i++) {
                var ran = Math.floor(Math.random() * arr.length);
                arrOut.push(arr[ran]);
                arr = (function (arr, ran) {
                    var arrOut = [];
                    for (var m = 0, n = arr.length; m < n; m++) {
                        if (arr[m] != arr[ran]) {
                            arrOut.push(arr[m]);
                        }
                    }
                    return arrOut;
                }(arr, ran));
            }
            return arrOut;
        }

2.从抽第二个起，新数组元素遍历比较当前随机元素，若抽到相同的则重抽

        function getDiffArr(arr, num) {
            var arrOut = [];
            var ran;
            for (var i = 0; i < num; i++) {
                ran = Math.floor(Math.random() * arr.length);
                // arrOut.push(arr[ran]);  // error
                arrOut[i]=arr[ran];
                if (i > 0) {
                    for (var m = 0; m < i; m++) {
                        if (arrOut[m] == arr[ran]) {
                            i--;
                            break;
                        }
                    }
                }

            }
            return arrOut;
        }

2.1  利用 flag 判定是否全不等

        var arr = [1, 2, 3, 4, 5, 6, 7, 8]

        function getDif(arr, num) {
            var arrOut = [];
            while (num > 0) {
                var ran = Math.floor(Math.random() * arr.length);                
                num--;
                if (arrOut.length > 0) {
                    var flag=false;
                    for (var i = 0; i < arrOut.length; i++) {
                        if (arrOut[i] == arr[ran]) {
                            num++;
                            flag=true;
                            break;
                        }
                    }
                    if(!flag){
                        arrOut.push(arr[ran]);
                    }                    
                }else{                    
                    arrOut.push(arr[ran]);
                }
            }

            return arrOut;
        }
        console.log(getDif(arr, 5));

3.利用对象属性唯一性与数组形成绑定关系  

        function getDiffArr(arr,num) {
            var hash = {};
            var arrOut = [];
            while (num > 0) {
                var ran = Math.floor(Math.random() * arr.length);
                if (!hash[ran]) {
                    hash[ran] = 1;
                    arrOut.push(ran);
                    num--;
                };
            }
            return arrOut;
        }

 3.1 不同的循环方式  

        var arr = [1, 2, 3, 4, 5, 6, 7, 8]

        function getDif(arr, num) {
            var arrOut = [];
            var hash = {};
            var len = arr.length;

            while(num){
                var ran = Math.floor(Math.random() *  len);
                if(!hash[ran]){
                    arrOut.push(arr[ran]);
                    hash[ran] = 1;   
                    num--;
                }
            }

            // for (var i = 0; i < num; i++) {
            //     var ran = Math.floor(Math.random() *  len);
            //     if (!hash[ran]) {
            //         arrOut.push(arr[ran]);
            //         hash[ran] = 1;                 
            //     }else{
            //         num++;
            //     }
            // }

            return arrOut;
        }
        console.log(getDif(arr, 5));

 4. 不断缩减数组长度，减少比较次数和排除抽取重复元素的可能

        var arr = [1, 2, 3, 4, 5, 6, 7, 8]

        function getDif(arr, num) {
            var arrOut = [];            
            for (var i = 0; i < num; i++) {
                var len=arr.length;
                var ran = Math.floor(Math.random() * len);
                arrOut[i] = arr[ran];
                arr[ran]=arr[len-1];
                arr.pop();   // arr=arr.slice(0,arr.length-1);

            }

            return arrOut;
        }
        console.log(getDif(arr, 5));

4.1 优化算法：规避数组长度操作

        var arr = [1, 2, 3, 4, 5, 6, 7, 8];
        function getDif(arr, num) {
            var arrOut = [];   
            var len=arr.length;         
            for (var i = 0; i < num; i++) {                
                var ran = Math.floor(Math.random() * (len-i));
                arrOut[i] = arr[ran];
                arr[ran]=arr[len-i-1];
            }
            return arrOut;
        }
        console.log(getDif(arr, 5));

 4.2 抽一个删一个

        var arr = [1, 2, 3, 4, 5, 6, 7, 8];

        function getDif(arr, num) {
            var arrOut = [];
            for (var i = 0; i < num; i++) {
                var len = arr.length;
                var ran = Math.floor(Math.random() * len);
                arrOut[i] =  arr.splice(ran, 1)[0];
               
            }
            return arrOut;
        }
        console.log(getDif(arr, 5));