php data structures and algorithms

This article mainly shares the PHP data structure and algorithm with you, mainly in the form of code, hoping to help everyone.

Data Structures and Algorithms

1. To enable objects to perform foreach loops like arrays, the properties must be private. (PHP5 implementation of Iterator mode, write a class to implement the Iterator interface) (Tencent)

<?php
    class Test implements Iterator{    private $item = array(&#39;id&#39;=>1,'name'=>'php');    public function rewind(){
        reset($this->item);
    }    public function current(){        return current($this->item);
    }    public function key(){        return key($this->item);
    }    public function next(){        return next($this->item);
    }    public function valid(){        return($this->current()!==false);
    }
}    //测试
    $t=new Test;    foreach($t as $k=>$v){        echo$k,'--->',$v,'<br/>';
    }?>

2. Use PHP to implement a two-way queue (Tencent)

<?php
    class Deque{    private $queue=array();    public function addFirst($item){        return array_unshift($this->queue,$item);
    }    public function addLast($item){        return array_push($this->queue,$item);
    }    public function removeFirst(){        return array_shift($this->queue);
    }    public function removeLast(){        return array_pop($this->queue);
    }
}?>

3. Please use bubble sorting method Sort the following set of data 10 2 36 14 10 25 23 85 99 45.

<?php
    // 冒泡排序
    function bubble_sort(&$arr){        for ($i=0,$len=count($arr); $i < $len; $i++) {            for ($j=1; $j < $len-$i; $j++) {                if ($arr[$j-1] > $arr[$j]) {
                    $temp = $arr[$j-1];
                    $arr[$j-1] = $arr[$j];
                    $arr[$j] = $temp;
                }
            }
        }
    }    // 测试
    $arr = array(10,2,36,14,10,25,23,85,99,45);
    bubble_sort($arr);
    print_r($arr);?>

4. Write a sorting algorithm (write code) and tell how to optimize it. (Sina)

<?php
    //快速排序
    function partition(&$arr,$low,$high){
        $pivotkey = $arr[$low];        while($low<$high){            while($low < $high && $arr[$high] >= $pivotkey){
                $high--;
            }
            $temp = $arr[$low];
            $arr[$low] = $arr[$high];
            $arr[$high] = $temp;            while($low < $high && $arr[$low] <= $pivotkey){
                $low++;
            }
            $temp=$arr[$low];
            $arr[$low]=$arr[$high];
            $arr[$high]=$temp;
        }        return$low;
    }function quick_sort(&$arr,$low,$high){    if($low < $high){
        $pivot = partition($arr,$low,$high);
        quick_sort($arr,$low,$pivot-1);
        quick_sort($arr,$pivot+1,$high);
    }
}?>

This algorithm is implemented through divide-and-conquer recursion. Its efficiency depends largely on the selection of reference elements. You can choose the middle element of the array, or you can get three elements randomly, and then Select the middle element (median of three numbers).
Another point is that when we are dividing, if the length of the divided subsequence is very small (less than 5 to 20), the efficiency of recursive sorting is usually not as fast as insertion sorting or Hill sorting. . Therefore, you can judge the length of the array. If it is less than 10, use insertion sort directly instead of calling this quick sort recursively.

5. A group of monkeys line up in a circle and are numbered according to 1, 2,..., n. Then start counting from the 1st one, count to the mth one, kick it out of the circle, start counting from behind it, count to the mth one, kick it out..., and continue in this way. Until there is only one monkey left, that monkey is called the king. Programming is required to simulate this process, input m, n, and output the number of the last king. (Sina) (Xiaomi)

This is the famous Joseph Ring problem

<?php
    // 方案一，使用php来模拟这个过程
    function king($n,$m){
        $mokey = range(1, $n);
        $i = 0;        while (count($mokey) >1) {
            $i += 1;
            $head = array_shift($mokey);//一个个出列最前面的猴子
            if ($i % $m !=0) {                #如果不是m的倍数，则把猴子返回尾部，否则就抛掉，也就是出列
                array_push($mokey,$head);
            }            // 剩下的最后一个就是大王了
            return $mokey[0];
        }
    }    // 测试
    echo king(10,7);    // 方案二，使用数学方法解决
    function josephus($n,$m){
        $r = 0;        for ($i=2; $i <= $m ; $i++) {
            $r = ($r + $m) % $i;
        }        return $r+1;
    }    // 测试
    print_r(josephus(10,7));?>

6. Write a two-dimensional array sorting algorithm function that can be universal and can call PHP built-in functions.

<?php//二维数组排序，$arr是数据，$keys是排序的健值，$order是排序规则，1是降序，0是升序function array_sort($arr,$keys,$order=0){    if(!is_array($arr)){        return false;
    }
    $keysvalue=array();    foreach($arr as $key => $val){
        $keysvalue[$key] = $val[$keys];
    }    if($order == 0){
        asort($keysvalue);
    }else{
        arsort($keysvalue);
    }
    reset($keysvalue);    foreach($keysvalue as $key => $vals){
        $keysort[$key] = $key;
    }
    $new_array=array();    foreach($keysort as $key=> $val){
        $new_array[$key]=$arr[$val];
    }    return$new_array;
}    //测试
    $person=array(        array('id'=>2,'name'=>'zhangsan','age'=>23),        array('id'=>5,'name'=>'lisi','age'=>28),        array('id'=>3,'name'=>'apple','age'=>17)
    );
    $result = array_sort($person,'name',1);
    print_r($result);?>

7. Use the binary method to find a sorted linear table of length 10. When the search is unsuccessful, the maximum number of comparisons required is (Xiaomi)

4

8. Randomly select three different numbers from these ten numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. The probability that "the three numbers do not contain 0 and 5" Yes (Xiaomi)

7/15

9. There are three mice at the three vertices of a triangle. When a gunshot is heard, the three mice begin to move at a constant speed along the sides of the triangle. How did they meet? The probability is (Xiaomi)

75%. Each mouse has two directions of movement: clockwise and counterclockwise. There are 8 types of movement conditions for 3 mice. Only when all 3 mice are moving clockwise or counterclockwise , they will not meet, and the remaining 6 situations will meet, so the probability of meeting is 6/8=75%.

10.描述顺序查找和二分查找（也叫做折半查找）算法，顺序查找必须考虑效率，对象可以是一个有序数组（小米）

<?php
    /**
     * 顺序查找
     * @param  array $arr 数组
     * @param   $k   要查找的元素
     * @return   mixed  成功返回数组下标，失败返回-1
     */
    function seq_sch($arr,$k){        for ($i=0,$n = count($arr); $i < $n; $i++) {            if ($arr[$i] == $k) {                break;
            }
        }        if($i < $n){            return $i;
        }else{            return -1;
        }
    }    /**
     * 二分查找，要求数组已经排好顺序
     * @param  array $array 数组
     * @param  int $low   数组起始元素下标
     * @param  int $high  数组末尾元素下标
     * @param   $k     要查找的元素
     * @return mixed        成功时返回数组下标，失败返回-1
     */
    function bin_sch($array,$low,$high,$k){        if ($low <= $high) {
            $mid = intval(($low + $high) / 2);            if ($array[$mid] == $k) {                return $mid;
            } elseif ($k < $array[$mid]) {                return bin_sch($array,$low,$mid - 1,$k);
            } else{                return bin_sch($array,$mid + 1,$high,$k);
            }
        }        return -1;
    }    // 测试：顺序查找
    $arr1 = array(9,15,34,76,25,5,47,55);    echo seq_sch($arr1,47);//结果为6

    echo "<br />";    // 测试：二分查找
    $arr2 = array(5,9,15,25,34,47,55,76);    echo bin_sch($arr2,0,7,47);//结果为5?>

11.我们希望开发一款扑克游戏，请给出一套洗牌算法，公平的洗牌并将洗好的牌存储在一个整形数组里。（鑫众人云）

<?php
    $card_num = 54;//牌数
    function wash_card($card_num){
        $cards = $tmp = array();        for($i = 0;$i < $card_num;$i++){
            $tmp[$i] = $i;
        }        for($i = 0;$i < $card_num;$i++){
            $index = rand(0,$card_num-$i-1);
            $cards[$i] = $tmp[$index];            unset($tmp[$index]);
            $tmp = array_values($tmp);
        }        return $cards;
    }    // 测试：
    print_r(wash_card($card_num));?>

12.写出你所知道的排序方法（亿邮）

冒泡排序，快速排序，插入排序，选择排序。

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