CareerCup

if(str[i]=='T'&&str[i+1]=='U'
{
str[i]='K';
str[i+1]='O'
}

We can use "Knuth Morris" algorithm to find the pattern index and then replace the whole required word ("TU" in this case) by required string..

It's so interesting that for the same position from same companies... some ppl get easy questions some ppl get crazy ones (that require specific knowledge of things like Fenwick trees).

No wonder Peter Norvig said when he reviewed Google's hiring process and claimed it was very random (actually he said the ppl who scored the best were worse employees than the ones who barely got in).

var result = 'STUN'.replace('TU', 'KO');
alert(result);

var string = "fklj";

for(var i=0; i < string.length; i++){
    if(string[i] === "k" && string[i+1] === "l"){
        string = string.slice(0, i) + 'zy' + string.slice(i+2);
    }
}

console.log(string)

function popString(string, find, replace){
	return string.replace(find, replace);
}
popString('STUN','TU','KO');