why recursion function returns "NaN" here-CodePudding

I have to find the sum of the absolute difference between consecutive elements of the array. But sumAbsArr function returns nun

var arr = [1, 5, 2];
var n = 3;
var cur = 0;

console.log(sumAbsArr(arr, n, cur))

function sumAbsArr(arr, n, cur) {
  if (n == cur) {
    return 0
  }
  var abs = Math.abs(arr[cur] - arr[cur   1])
  var ans = abs   sumAbsArr(arr, n, cur   1)
  return ans
}

CodePudding user response：

I think you are wrong at placing the condition. Look at arr[cur 1] (at line 11), when cur = 3 the cur 1 is out of range (arr index is start at 0 and end at arr.length-1 which is 2). So to prevent arr[cur 1] have NaN value, you have to change the condition

var arr = [1, 5, 2];
var n = 3;
var cur = 0;

console.log(sumAbsArr(arr, n, cur))

function sumAbsArr(arr, n, cur) {
  // change the condition to stay within the range
  if (cur == n-1) { 
    return 0
  }
  var abs = Math.abs(arr[cur] - arr[cur   1])
  var ans = abs   sumAbsArr(arr, n, cur 1)
  return ans
}