Time out error (array is subsequence of another array)

Question

I wrote this code in my computer's IDE and passed all test cases I could think of. However, after testing it out on AlgoExpert and LeetCode, I'm getting a Time Out error. I've wracked my brain trying to come up any test cases I could've missed, but cannot seem to think of any. I've also tried testing out all the test cases they give me in AlgoExpert. Hopefully I'm not missing anything obvious... Any tips from someone will be much appreciated!

Given 2 non-empty array of integers, write a function that determines whether the second array is a subsequence of the first. Note that a single number in an array or the array itself are both valid subsequences of the array.

function isValidSubsequence(array, sequence) {
    if (sequence.length > array.length) return false;
    let s = 0;
    let a = 0;
    
    while (s < sequence.length){
        if (array[a] === sequence[s]){
            s++;
            a++
        }
        else a++;
        if (s !== sequence.length - 1 && a === array.length - 1) return false;
    }
    return true;
}

score 3 · Answer 1 · answered Apr 20 '21 at 00:58

Your algorithm does not return at the end if the sequence fails.

// running this will freeze your browser
function isValidSubsequence(array, sequence) {
    if (sequence.length > array.length) return false;
    let s = 0;
    let a = 0;
    
    while (s < sequence.length){
        if (array[a] === sequence[s]){
            s++;
            a++
        }
        else a++;
        if (s !== sequence.length - 1 && a === array.length - 1) return false;
    }
    return true;
}

console.log(isValidSubsequence([1, 2, 3], [5]));

For what you're trying to do, you probably want a nested loop to check if the sequence matches, starting at an index in the array (starting the sequence index from 0):

function isValidSubsequence(array, sequence) {
    let s = 0;
    
    outer:
    while (s < array.length){
        for (let i = 0; i < sequence.length; i++) {
            if (array[s + i] !== sequence[i]){
                s++;
                continue outer;
            }
            return true;
        }
        s++;
    }
    return false;
}

console.log(isValidSubsequence([1, 2, 3], [5]));

But I think .includes would be easier:

const isValidSubsequence = (array, sequence) => array.join().includes(sequence.join());

console.log(isValidSubsequence([1, 2, 3], [5]));
console.log(isValidSubsequence([1, 2, 3], [2, 3]));

Time out error (array is subsequence of another array)

1 Answers1