strCompression, Javascript

strCompression

//JavaScript-C24.2.0 (SpiderMonkey)

print(strCompression('aaabbbcccccaa'));
print(strCompression2('aaabbbcccccaa'));

// string compression algo
// aaabbbcccccaa -> a3b3c4a2
function strCompression(str) {
  if (str.length == 0) return '';
  
  let newStr = '';
  let count = 0;
  let prevChar = str[0];
  for (let i = 0; i < str.length; i++) {
    if (str[i] !== prevChar) {
      newStr += str[i-1] + count;
      prevChar = str[i];
      count = 0;
    }
    count++;
    
    if (i === str.length-1) {
      newStr += str[i] + count;
    }
  }
  
  return newStr;
}

// to simulate a string buffer, build an array of characters and do a join
function strCompression2(str) {
  if (str.length == 0) return '';
  
  let newStr = [];
  let count = 0;
  let prevChar = str[0];
  for (let i = 0; i < str.length; i++) {
    if (str[i] !== prevChar) {
      newStr.push(str[i-1] + count);
      prevChar = str[i];
      count = 0;
    }
    count++;
    
    if (i === str.length-1) {
      newStr.push(str[i] + count);
    }
  }
  
  return newStr.join('');
}


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