Find longest occurrence of same number in array

Question

Using JavaScript, I'm trying to find a way to find the longest occurrence of the same number (in this case, 1) in an array.

For instance, here's a sample array: [2,5,3,1,1,1,3,7,9,6,4,1,1,1,1,1,4,7,2,3,1,1,4,3]

I'd like to write a function that would return "5", since the number 1 occurs 5 times in a row. (It also occurs 3 and 2 times in a row, but I'm after the longest occurrence).

So far, I have written:

function streak(arr) {
    var i,
        temp,
        streak,
        length = arr.length;

    for(i=0; i<length; i++) {
        if (arr[i] === 1) {
            streak += 1;
        } else {
            temp = streak;
            break;
        }
    }
}

I know I need some way of knowing where I left off if I find an occurrence, but I'm feeling kind of stuck.

Any pointers?

Answer 1

I've modified your function slightly. You need to store the highest streak as a separate variable from the current streak, and overwrite that where necessary in your loop - finally returning that variable at the end of your function.

function streak(arr) {
    var i,
        temp,
        streak,
        length = arr.length,
        highestStreak = 0;

    for(i = 0; i < length; i++) {
        // check the value of the current entry against the last
        if(temp != '' && temp == arr[i]) {
            // it's a match
            streak++;
        } else {
            // it's not a match, start streak from 1
            streak = 1;
        }

        // set current letter for next time
        temp = arr[i];

        // set the master streak var
        if(streak > highestStreak) {
            highestStreak = streak;
        }
    }

    return highestStreak;
}

var array = [2,5,3,1,1,1,3,7,9,6,4,1,1,1,1,1,4,7,2,3,1,1,4,3];

console.log(streak(array)); // 5

And if you want to also track what the value of the highest streak was, define another variable at the start of your function, save the value of it when you save the highest streak, and return it as an array:

    // set the master streak var
    if(streak > highestStreak) {
        highestStreakValue = temp;
        highestStreak = streak;
    }
}

return [highestStreak, highestStreakValue];


var array = [2,5,3,1,1,1,3,7,9,6,4,'a','a','a','a','a',4,7,2,3,1,1,4,3];
console.log(streak(array)); // [5, "a"]

Demo returning both

Answer 2

An alternative approach. I'm converting the array to a string. The regular expression has a backrefence, which ensures that only sequences of the same character are matched. Also when exec is used with the g flag, repeated executions will continue from the end of last match, and not from the beginning.

var arr = [2,5,3,1,1,1,3,7,9,6,4,1,1,1,1,1,4,7,2,3,1,1,4,3];
var str = arr.join('');
var regex = /(.)\1*/g;
var match;
var largest = '';

while (match = regex.exec(str)) {
  largest = match[0].length > largest.length ? match[0] : largest;
}

console.log(largest.length);