Linear search

JavaScript · Unit 22: Searching and sorting

Full plan
JavaScript
10 exercises

Searching an array means asking one element at a time until you hit what you want. The moment it matches, you return the position and you're out.

If the loop ends with no match, it wasn't there: you return -1, the same signal indexOf uses.

function search(nums, v) {
  const n = nums.length;
  for (let i = 0; i < n; i++) {
    if (nums[i] === v) {
      return i;
    }
  }
  return -1;
}
console.log(search([4, 8, 5], 8));

Prints

The rest of the explanation is in the lesson, which is part of the full plan.

Exercises in this lesson

You do them in the app, which checks them on the spot and explains why.

1. Predict the output
The same array gets searched twice. What does it print?
2. Complete the code
Complete it so the function tells you which position the 8 is at.
3. Multiple choice
What does this function do?
4. Predict the output
steps counts the comparisons of each search. What does it print?
5. Find the bug
search should give the position of the first fig, which is 0. Which line has the error?
6. Complete the code
Complete it to find where in the line the person with id 4 is standing.
7. Put the lines in order
Put search in order: it returns the position of v, or -1 if it isn't there.
8. Find the case that fails
position(nums, v) returns the position where v first shows up, or -1 if it isn't there. Which call does it fail on?
9. Predict the output
The walk looks for the highest score. What does it print?
10. Multiple choice
An unsorted list of 100 names. Searching one by one, how many comparisons can finding one cost?

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