Array Traversal Patterns

Written by Swapnil RajaPublished 28 Aug 2026

Most array problems are one of four walks. Recognising which one you need is faster than inventing a solution from scratch.

1. Single pass with running state

Carry one value through the array and update it as you go. Works whenever the answer depends only on what you have already seen.

Running total and best run

javascript

function largest(items) {
  let best = items[0]
  for (const n of items) {
    if (n > best) best = n
  }
  return best
}

// Largest sum of any run of consecutive numbers.
function bestRun(items) {
  let best = items[0]
  let current = items[0]

  for (let i = 1; i < items.length; i++) {
    current = Math.max(items[i], current + items[i])
    best = Math.max(best, current)
  }

  return best
}

console.log(bestRun([-2, 1, -3, 4, -1, 2, 1, -5, 4]))  // 6

PreviousArrays in JavaScript for DSA NextStrings in JavaScript for DSA

Both ends

javascript

function isPalindrome(items) {
  let left = 0
  let right = items.length - 1

  while (left < right) {
    if (items[left] !== items[right]) return false
    left++
    right--
  }

  return true
}

Remove in place

javascript

// Strip out every zero without creating a new array.
function removeZeros(items) {
  let write = 0

  for (let read = 0; read < items.length; read++) {
    if (items[read] !== 0) {
      items[write] = items[read]
      write++
    }
  }

  items.length = write
  return items
}

console.log(removeZeros([0, 1, 0, 3, 12]))  // [1, 3, 12]

Array Traversal Patterns

1. Single pass with running state

2. Two indices from both ends

3. Two indices moving forward

4. Remember what you have seen

Choosing between them