编写一个函数，叫做 sample(arr,n)可以从 arr 中返回 n 项样本。
function sample(arr,n){
var idxArr = []
var result = []
while(result.length != n){
var idx = parseInt(Math.random()*arr.length);
// includes方法判断idxArr是否包含idx
if (!idxArr.includes(idx)) {
result.push(arr[idx])
idxArr.push(idx)
}
}
return result
}
let a = [1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,6,6,6,6,7,7,7,7,8,8,8,8,9,9,9,9,10,10,10,10,11,11,11,11,12,12,12,12,13,13,13,13,14,14,14,14,15,15,15,15,16,16,16,16,17,17,17,17,18,18,18,18,19,19,19,19,20,20,20,20]
console.log(sample(a,15));// [17, 18, 10, 13, 2, 7, 4, 1, 5, 10, 20, 8, 20, 4, 15]
