javascript - 从 n 到 m 的偶数之和，无论 n<m 还是 n>m

Question

我正在尝试计算来自 n 的数字总和至 m ，无论是否 n>m或 n<m .我只设法让它在 n<m 时工作. 有人可以给我一个帮助/提示吗？

       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);
}

Answer 1

尝试

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>