Recursion Sum Two Dimensional Array

Question

function twoDSum(arr){
      debugger
      result = 0
      for (let i = 0; i < arr.length; i++) {
        if (Array.isArray(arr[i])) {
         result += twoDSum(arr[i])
        } else {
          result += arr[i]
        }
      }
      return result
    }
    
    array_1 = [
      [4, 5],
      [1, 3, 7, 1]
    ]
    console.log(twoDSum(array_1))

The code above works perfectly. However, my question is why the code below will produce the wrong answer. I assume I am computing the sum of the sub-array and store it into a variable and add it to my result instead, it is doubling on every single array

function twoDSum(arr){
      debugger
      result = 0
      for (let i = 0; i < arr.length; i++) {
        if (Array.isArray(arr[i])) {
         let subSum = twoDSum(arr[i])
         result += subSum
        } else {
          result += arr[i]
        }
      }
      return result
    }
    
    array_1 = [
      [4, 5],
      [1, 3, 7, 1]
    ]
    console.log(twoDSum(array_1))

Note you have a global variable `result` and all the recursion steps adds values to it. — Shidersz, Mar 05 '19 at 20:21

score 0 · Answer 1 · answered Mar 05 '19 at 20:05

Use a local result variable instead of a global :

function twoDSum(arr){
      debugger
      let result = 0
      for (let i = 0; i < arr.length; i++) {
        if (Array.isArray(arr[i])) {
         let subSum = twoDSum(arr[i])
         result += subSum
        } else {
          result += arr[i]
        }
      }
      return result
    }
    
    array_1 = [
      [4, 5],
      [1, 3, 7, 1]
    ]
    console.log(twoDSum(array_1))

Recursion Sum Two Dimensional Array

1 Answers1