PHP counts the number of times a number appears in a sorted array

This article mainly introduces PHP's method of counting the number of occurrences of a number in a sorted array. It involves PHP's related operating skills for searching and counting in arrays based on the binary search algorithm. Friends who need it can refer to it. I hope it can help. Everyone.

Question

Count the number of times a number appears in a sorted array.

Solution

Since it is a sorted array, binary search is the most efficient. After you find it, expand it to both sides.

Code

##

<?php
function GetNumberOfK($data, $k)
{
  if(count($data)==0){
    return 0;
  }
  $index = 0;
  $low = 0;
  $high = count($data)-1;
  $middle = 0;
  //二分查找找到k的index
  while($low<=$high){
    $middle = ($high+$low)>>1;
    if($data[$middle]==$k){
      $index = $middle;
      break;
    }
    else if($data[$middle]>$k) {
      $high = $middle -1;
    }else{
      $low = $middle+1;
    }
    $index = -1;
  }
  // console.log(index);
  // 如果没找到
  if($index==-1){
    return 0;
  }
  //找到了 分别往左右查找边界
  $start = $index;
  $end = $index;
  $count = 0;
  while($data[$start]==$k){
    $count++;
    $start--;
  }
  while($data[$end]==$k){
    $count++;
    $end++;
  }
  return $count-1;
}

Related recommendations:

Problems related to user-defined sorted array

In the sorted array, find the number of occurrences of a given number. For example, in [1, 2, 2, 2, 3]

Reorder the array according to a certain key value

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