The stuck sensor

Problem

In the lab, a healthy sensor changes its reading almost every second. When it gets stuck, it repeats the same one several times in a row, and the technician wants to know which value it stayed stuck on the longest. Write a function that takes the list of readings (whole numbers, which can be negative; the list is never empty) and returns the value of the longest run of equal readings in a row. Return the value, not how long it lasted. With [4, 7, 7, 7, 2, 2, 7] the longest run is the three 7s: you return 7. Only readings in a row count: in [3, 8, 3, 8, 3, 6, 6] the 3 shows up three times, but never two together, and 6 wins.

If two runs tie in length, the one that came first wins. If no reading repeats, every run has length 1: return the first reading.

Examples

• The example

  [4, 7, 7, 7, 2, 2, 7] → 7

• Most frequent is not longest in a row

  [3, 8, 3, 8, 3, 6, 6, 3] → 6

• A single reading

  [9] → 9

• None repeats

  [4, 1, 8] → 4

• A tie, the first one wins

  [2, 2, 5, 5] → 2

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def stuck_value(readings):
    pass

function stuckValue(readings) {
}