javascript - 从n到m的偶数和，无论n <m还是n> m

我试图计算从n到m的数字和，不管是n>m还是n<m。我只有在n<m的时候才能让它工作。
有人能帮我个忙吗？

       function SumEvenN()
{
    var n = getFirstNumber();
    var m = getSecondNumber();

    var s = 0;

    if (n<m)
    {
        min = n;
        max = m;
    }
    else if (m<n)
    {
        min = m;
        max = n;
    }

    if (n>m)
    {
        [n, m] = [m, n]
    }
    for (var i = 2; i<=m; i++)
    {
        if (i % 2 == 0)
        {
            s += i;
        }
    }
    alert(s);

}


function getFirstNumber()
{
    var a = document.getElementById("first-number");
    return parseInt(a.value);
}

function getSecondNumber()
{
    var b = document.getElementById("second-number");
    return parseInt(b.value);
}

最佳答案

三

function SumEvenN(n,m) {
  if(n>m) [n, m] = [m, n];  // swap variables if n>m
  n=n%2 ? n+1 : n;          // if n is odd add 1 to it
  m=m%2 ? m-1 : m;          // if m is odd add -1 to it
  let t=(m-n+2)/2;          // number of even elements between n and m
  return t*(n+m)/2;         // use formula of arithmetic progression sum
}

function SumEvenN(n,m) {
  if(n>m) [n, m] = [m, n];  // swap variables if n>m
  n=n%2 ? n+1 : n;          // if n is odd add 1 to it
  m=m%2 ? m-1 : m;          // if m is odd add -1 to it
  let t=(m-n+2)/2;          // number of even elements between n and m
  return t*(n+m)/2;         // use foruma of arithmetic progression sum
}

function calc() {
  console.log(SumEvenN(+first.value, +second.value) );
}

<input id="first" type="number" value="9"/>
<input id="second" type="number" value="16"/>
<button id="btn" onclick="calc()">Calc</button>

关于javascript - 从n到m的偶数和，无论n <m还是n> m，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/56227401/