经典算法

 1 function BubbleSort(&$arr){
 2     for($i=0;$i<count($arr);$i++){
 3         for($j=$i+1;$j<count($arr);$j++){    
 4             if($arr[$i]<$arr[$j]){
 5                 $temp=$arr[$i];
 6                 $arr[$i]=$arr[$j];
 7                 $arr[$j]=$temp;
 8             }
 9         }
10     }
11     return $arr;
12 }
冒泡排序
 1 $arr=[3,5,1,3,7,8,9,5,0,5];
 2 QuickSort($arr,0,count($arr)-1);
 3 echo json_encode($arr);
 4 function QuickSort(&$arr,$left,$right){
 5     if($left<$right){
 6         $key=$arr[$left];
 7         $low=$left;
 8         $high=$right;
 9         while ($low < $high) {
10             while ($arr[$high] >= $key && $low < $high) {
11                 $high --;
12             }
13             $arr[$low]=$arr[$high];
14             while ($arr[$low] <= $key && $low < $high) {
15                $low ++;
16             }
17             $arr[$high]=$arr[$low];
18         }
19         $arr[$low]=$key;
20         QuickSort($arr,$left,$low-1);
21         QuickSort($arr,$low+1,$right);
22     }
23 }
快速排序
 1 $arr1=[0,3,5,5,7,8,9,20,30,57];
 2 echo binarySearch($arr1,20);
 3 function binarySearch($arr,$element){
 4     $left = 0;
 5     $right = count($arr)-1;
 6     while ($left<$right){
 7         $mid =round(($left+$right)/2);
 8         if($arr[$mid]>$element){
 9             $right = $mid-1;
10 
11         }else if($arr[$mid]<$element){
12             $left = $mid+1;
13         }else{
14             return $mid;
15         }
16     }
17     return -1;
18 }
折半查找
 1 function moveTower($n,$A="A",$B="B",$C="C"){
 2         if($n==1){
 3             echo "{$n}:{$A}-->{$C}
";
 4         }else{
 5             //将最上面的n-1个从A通过C移动到B
 6             $this->moveTower($n-1,$A,$C,$B);
 7             //将最下面第n个最大的盘子直接从A移动到C
 8             echo "{$n}:{$A}-->{$C}
";
 9             //再将现在都在B上的n-1个从B通过A移动到C上
10             $this->moveTower($n-1,$B,$A,$C);
11         }
12     }
汉诺塔递归
 1 class StackByQueue{
 2     private $queue1=null;
 3     private $queue2=null;
 4     function __construct()
 5     {
 6         $this->queue1 = new SplQueue();
 7         $this->queue2 = new SplQueue();
 8     }
 9     function __destruct()
10     {
11         $this->queue1=null;
12         $this->queue2=null;
13     }
14 
15     public function Pop(){
16         if($this->queue1->isEmpty()){
17             return null;
18         }
19         while($this->queue1->count()!=1){
20             $this->queue2->enqueue($this->queue1->dequeue());
21         }
22         $pop = $this->queue1->dequeue();
23         while(!$this->queue2->isEmpty()){
24             $this->queue1->enqueue($this->queue2->dequeue());
25         }
26         return $pop;
27 
28     }
29     public function Push($ele){
30         $this->queue1->enqueue($ele);
31     }
32 }
使用队列实现栈的功能
 1 class QueueByStack{
 2     private $stack1=null;
 3     private $stack2 = null;
 4     function __construct()
 5     {
 6         $this->stack1 = new SplStack();
 7         $this->stack2 = new SplStack();
 8     }
 9     function __destruct()
10     {
11         $this->stack1 = null;
12         $this->stack2 = null;
13     }
14 
15     public function EnQueue($ele){
16         $this->stack1->push($ele);
17     }
18     public function DeQueue(){
19         while(!$this->stack1->isEmpty()){
20             $this->stack2->push($this->stack1->pop());
21         }
22         if($this->stack2->isEmpty()){
23             return null;
24         }else{
25             $pop = $this->stack2->pop();
26             while(!$this->stack2->isEmpty()){
27                 $this->stack1->push($this->stack2->pop());
28             }
29             return $pop;
30         }
31     }
32 }
使用栈实现队列的功能
早晨一女生背着一堆书出了图书馆，结果警报响了，大妈让女生看看是哪本书把警报弄响了，那女生把书倒出来，准备一本一本的测。大妈见状急了，把书分成两份，第一份过了一下，响了。又把这一份分成两份接着测，三回就找到了，大妈用鄙视的眼神看着女生，仿佛在说O(n)和O(logn)都分不清。
结果图书馆丢了n-1本书。

class TreeNode
{
    public $number = 0;
    public $level = 0;
    public $originNumber = 0;

    public function __construct($originNumber0, $number0, $level0)
    {
        $this->number = $number0;
        $this->level = $level0;
        $this->originNumber = $originNumber0;
    }
}

function getHalf(TreeNode $treeNode, &$arr)
{
    $maxLevel = 4;
    $number = $treeNode->number;
    $level = $treeNode->level;
    $originNumber = $treeNode->originNumber;
    $a_half = intval($number / 2);
    $b_half = $number - $a_half;
    $level++;
    if ($level > $maxLevel || $a_half == 0 || $b_half == 0) {
        return;
    }
    if (($a_half == 1 && $level == $maxLevel) || ($b_half == 1 && $level == $maxLevel)) {
        !in_array($originNumber, $arr) && $arr[] = $originNumber;
        return;
    }
    if ($a_half > 1) {
        getHalf(new TreeNode($originNumber, $a_half, $level), $arr);
    }
    if ($b_half > 1) {
        getHalf(new TreeNode($originNumber, $b_half, $level), $arr);
    }
}

$arr0 = [];
for ($i = 0; $i < 1000; $i++) {
    getHalf(new TreeNode($i, $i, 0), $arr0);
}
echo json_encode($arr0);die;

输出：
[9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31]
求一个脑筋急转弯的N是多少
  1 class STreeNode
  2 {
  3     public $level = 0;
  4     public $leftChild = null;
  5     public $rightChild = null;
  6     public $parent = null;
  7     public $key = null;
  8     public $data = null;
  9 }
 10 
 11 class STree
 12 {
 13 
 14     public $root = null;
 15 
 16     public function __construct(STreeNode $root)
 17     {
 18         $this->root = $root;
 19     }
 20 
 21     /**
 22      * @desc: 二叉树节点插入
 23      * @author: 流火行者
 24      * @date: 2019/3/12 6:41 PM
 25      * ---------------------------------
 26      * 支付宝首页搜“510992378”查看留言
 27      * ---------------------------------
 28      * @param STreeNode $childNode
 29      * @param STreeNode $parentNode
 30      */
 31     public function insert(STreeNode $childNode, STreeNode $parentNode)
 32     {
 33         $childNode->level = $parentNode->level + 1;
 34         $childNode->parent = $parentNode;
 35         $childNode->data = [];
 36         if ($childNode->key > $parentNode->key) {
 37             if ($parentNode->rightChild == null) {
 38                 $parentNode->rightChild = $childNode;
 39             } else {
 40                 $this->insert($childNode, $parentNode->rightChild);
 41             }
 42         } else {
 43             if ($parentNode->leftChild == null) {
 44                 $parentNode->leftChild = $childNode;
 45             } else {
 46                 $this->insert($childNode, $parentNode->leftChild);
 47             }
 48         }
 49     }
 50 
 51     public function search($key, STreeNode $parentNode = null, &$list = [])
 52     {
 53         if ($parentNode == null) return;
 54         if ($key == $parentNode->key) {
 55             $list[] = $parentNode;
 56         } else {
 57             $this->search($key, $parentNode->leftChild, $list);
 58             $this->search($key, $parentNode->rightChild, $list);
 59         }
 60     }
 61 
 62     public function delete()
 63     {
 64 
 65     }
 66 
 67     /**
 68      * @desc: 递归前序遍历
 69      * @author: 流火行者
 70      * @date: 2019/3/12 6:41 PM
 71      * ---------------------------------
 72      * 支付宝首页搜“510992378”查看留言
 73      * ---------------------------------
 74      * @param STreeNode|null $node
 75      */
 76     public function preOrderTraverse(STreeNode $node = null)
 77     {
 78         if ($node == null) return;
 79         echo $node->key . PHP_EOL;
 80         $this->inOrderTraverse($node->leftChild);
 81         $this->inOrderTraverse($node->rightChild);
 82     }
 83 
 84     public function preOrderTraverseLoop()
 85     {
 86         $stack = new SplStack();
 87         $pNode = $this->root;
 88         while (!$stack->isEmpty() || $pNode != null) {
 89             if ($pNode != null) {
 90                 echo $pNode->key . PHP_EOL;
 91                 $stack->push($pNode);
 92                 $pNode = $pNode->leftChild;
 93             } else {
 94                 $node = $stack->pop();
 95 
 96                 $pNode = $node->rightChild;
 97 
 98             }
 99         }
100     }
101 
102     /**
103      * @desc: 递归中序遍历
104      * @author: 流火行者
105      * @date: 2019/3/12 6:41 PM
106      * ---------------------------------
107      * 支付宝首页搜“510992378”查看留言
108      * ---------------------------------
109      * @param STreeNode|null $node
110      */
111     public function inOrderTraverse(STreeNode $node = null)
112     {
113         if ($node == null) return;
114         $this->inOrderTraverse($node->leftChild);
115         echo $node->key . '|level=' . $node->level . PHP_EOL;
116         $this->inOrderTraverse($node->rightChild);
117     }
118 
119     /**
120      * @desc: 循环中序遍历
121      * @author: 流火行者
122      * @date: 2019/3/12 6:40 PM
123      * ---------------------------------
124      * 支付宝首页搜“510992378”查看留言
125      * ---------------------------------
126      */
127     public function inOrderTraverseLoop()
128     {
129         $stack = new SplStack();
130         $pNode = $this->root;
131         while ($pNode != null || !$stack->isEmpty()) {
132             if ($pNode != null) {
133                 $stack->push($pNode);
134                 $pNode = $pNode->leftChild;
135             } else {
136                 $node = $stack->pop();
137                 echo $node->key . '|';
138                 $pNode = $node->rightChild;
139             }
140         }
141     }
142 
143     /**
144      * @desc: 后序遍历（递归）
145      * @author: 流火行者
146      * @date: 2019/3/12 6:40 PM
147      * ---------------------------------
148      * 支付宝首页搜“510992378”查看留言
149      * ---------------------------------
150      * @param STreeNode|null $node
151      */
152     public function postOrderTraverse(STreeNode $node = null)
153     {
154         if ($node == null) return;
155         $this->postOrderTraverse($node->leftChild);
156         $this->postOrderTraverse($node->rightChild);
157         echo $node->key . PHP_EOL;
158     }
159 
160     /**
161      * @desc: 循环后序遍历
162      * @author: 流火行者
163      * @date: 2019/3/12 6:58 PM
164      * ---------------------------------
165      * 支付宝首页搜“510992378”查看留言
166      * ---------------------------------
167      */
168     public function postOrderTraverseLoop()
169     {
170         //todo
171     }
172 
173     /**
174      * @desc: 层次遍历
175      * @author: 流火行者
176      * @date: 2019/3/12 6:40 PM
177      * ---------------------------------
178      * 支付宝首页搜“510992378”查看留言
179      * ---------------------------------
180      */
181     public function layerOrderTraverseLoop()
182     {
183         $queue = new SplQueue();
184         $queue->enqueue($this->root);
185         echo PHP_EOL;
186         while (!$queue->isEmpty()) {
187             $o = $queue->dequeue();
188             if (empty($o)) break;
189             echo 'key=' . $o->key . "#level=" . $o->level . PHP_EOL;
190             if ($o->leftChild != null) {
191                 $queue->enqueue($o->leftChild);
192             }
193             if ($o->rightChild != null) {
194                 $queue->enqueue($o->rightChild);
195             }
196         }
197     }
198 
199 }
200 
201 $arr = [3, 7, 2, 4, 6, 9];
202 //$arr = [2,7,3,6,9,2.5,4];
203 
204 //$arr = array_reverse($arr);
205 $rootNode = new STreeNode();
206 $rootNode->level = 0;
207 $rootNode->key = 5;
208 $rootNode->data = [];
209 $tree = new STree($rootNode);
210 foreach ($arr as $item) {
211     $node = new STreeNode();
212     $node->key = $item;
213     $node->data = [];
214     $tree->insert($node, $rootNode);
215 }
216 //$tree->inOrderTraverse($tree->root);
217 //$tree->inOrderTraverseLoop();
218 $tree->postOrderTraverse($rootNode);
219 echo PHP_EOL;
220 $tree->postOrderTraverseLoop();
221 //$tree->layerOrderTraverseLoop();
222 $list = [];
223 //$tree->search(37,$tree->root,$list);
二叉排序树 
 1 $list = [3, 5, 1, 2, 7, 3, 8, 2, 9];
 2 
 3 mergerSort($list, 0, count($list) - 1);
 4 
 5 function mergerSort(&$arr = [], $left, $right)
 6 {
 7     $mid = intval(($left + $right) / 2);
 8     if ($left < $right) {
 9         mergerSort($arr, $left, $mid);
10         mergerSort($arr, $mid + 1, $right);
11         echo 'left:'.json_encode(array_slice($arr, $left, $mid - $left + 1)) . PHP_EOL;
12         echo 'right:'.json_encode(array_slice($arr, $mid + 1, $right - $mid)) . PHP_EOL;
13         mergeArray($arr,$left,$mid,$right);
14     }
15 }
16 
17 function mergeArray(&$arr = [], $left, $mid, $right)
18 {
19     $i = $left;
20     $j = $mid + 1;
21     $k = 0;
22     $temp = [];
23     //有序两个数组合并
24     while ($i <= $mid && $j <= $right) {
25         if ($arr[$i] <= $arr[$j]) {
26             $temp[$k++] = $arr[$i++];
27         } else {
28             $temp[$k++] = $arr[$j++];
29         }
30     }
31     //左侧剩余的直接合并，左和右只可能有一个有剩余
32     while ($i <= $mid) {
33         $temp[$k++] = $arr[$i++];
34     }
35     //右侧剩余的直接合并
36     while ($j <= $right) {
37         $temp[$k++] = $arr[$j++];
38     }
39     //修改原数组
40     $k=0;
41     while ($left<=$right){
42         $arr[$left++] = $temp[$k++];
43     }
44     echo 'merge'.json_encode($temp) . PHP_EOL;
45     echo  PHP_EOL;
46 }
47 
48 输出：
49 left:[3]
50 right:[5]
51 merge[3,5]
52 
53 left:[3,5]
54 right:[1]
55 merge[1,3,5]
56 
57 left:[2]
58 right:[7]
59 merge[2,7]
60 
61 left:[1,3,5]
62 right:[2,7]
63 merge[1,2,3,5,7]
64 
65 left:[3]
66 right:[8]
67 merge[3,8]
68 
69 left:[2]
70 right:[9]
71 merge[2,9]
72 
73 left:[3,8]
74 right:[2,9]
75 merge[2,3,8,9]
76 
77 left:[1,2,3,5,7]
78 right:[2,3,8,9]
79 merge[1,2,2,3,3,5,7,8,9]
二路归并排序

未完待续....

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原文地址：https://www.cnblogs.com/JimmyBright/p/6669059.html