排列組合_排列_數學公式
阿新 • • 發佈:2018-12-26
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<script>
var arr = ['A', 'B', 'C'];
/*
* A(m,n) 從m中取出n個有多少種情況
* m!/(m-n)!
* */
function show(arr, num){
var len = arr.length;
if (num > len || num <= 0){
alert(arr + '中只能取出1~' + len + '個,而你想取出' + num + '個');
return;
}
return f(len) / f(len-num);
}
// 遞迴
function f(num){
if(num <= 1) return 1;
return num * f(num - 1);
}
console.log(show(arr, 2));
</script>
</body>
</html>