Top php interview questions

function reverseString($str) {
  
  return strrev($str);
}

function isPrime($num) {
  
  if ($num <= 1) {
    
    return false;
  }
  for ($i = 2;
  $i <= sqrt($num);
  $i++) {
    
    if ($num % $i == 0) {
      
      return false;
    }
  }
  return true;
}

function findMax($arr) {
  
  return max($arr);
}

function sortArray($arr) {
  
  sort($arr);
  return $arr;
}

function findFirstDuplicate($arr) {
  
  $seen = array();
  foreach ($arr as $num) {
    
    if (in_array($num, $seen)) {
      
      return $num;
    }
    $seen[] = $num;
  }
  return null;
}

function findMissingNumber($arr) {
  
  $n = count($arr) + 1;
  $sum = $n * ($n + 1) / 2;
  $actualSum = array_sum($arr);
  return $sum - $actualSum;
}

function findLongestCommonPrefix($strs) {
  
  $prefix = $strs[0];
  for ($i = 1;
  $i < count($strs);
  $i++) {
    
    while (strpos($strs[$i], $prefix) !== 0) {
      
      $prefix = substr($prefix, 0, -1);
    }
  }
  return $prefix;
}

function findMostFrequent($arr) {
  
  $freq = array_count_values($arr);
  arsort($freq);
  return key($freq);
}

function findSecondLargest($arr) {
  
  $max = $secondMax = PHP_INT_MIN;
  foreach ($arr as $num) {
    
    if ($num > $max) {
      
      $secondMax = $max;
      $max = $num;
    }
    elseif ($num > $secondMax && $num != $max) {
      
      $secondMax = $num;
    }
  }
  return $secondMax;
}

function findFirstNonRepeating($str) {
  
  $freq = array_count_values(str_split($str));
  foreach (str_split($str) as $char) {
    
    if ($freq[$char] == 1) {
      
      return $char;
    }
  }
  return null;
}

function findMinWindow($str, $target) {
  
  $targetCount = array_count_values(str_split($target));
  $required = count($targetCount);
  $left = 0;
  $minLen = PHP_INT_MAX;
  $minWindow = '';
  $formed = 0;
  $windowCounts = array();
  for ($right = 0;
  $right < strlen($str);
  $right++) {
    
    $char = $str[$right];
    if (isset($targetCount[$char])) {
      
      $windowCounts[$char] = isset($windowCounts[$char]) ? $windowCounts[$char] + 1 : 1;
      if ($windowCounts[$char] == $targetCount[$char]) {
        
        $formed++;
      }
    }
    while ($left <= $right && $formed == $required) {
      
      $char = $str[$left];
      if ($right - $left + 1 < $minLen) {
        
        $minLen = $right - $left + 1;
        $minWindow = substr($str, $left, $right - $left + 1);
      }
      if (isset($targetCount[$char])) {
        
        $windowCounts[$char]--;
        if ($windowCounts[$char] < $targetCount[$char]) {
          
          $formed--;
        }
      }
      $left++;
    }
  }
  return $minWindow;
}