PHP实现四种排序

程序=算法+数据结构，作为一个PHP程序员，需要掌握一下。

/**
*   冒泡排序
*   按照两两比较大小，注意比较轮数和每轮比较次数；
*   假设数组有n个元素，则需要n-1轮比较；每i轮比较n-i次（即 第1轮中需要n-1次比较、第2轮中需要n-2次比较...第n-1轮中需要1次比较）
*/
function numSort($arr){
    $mnt = count($arr);
    if($mnt==1){
        return $arr;
    }
    for ($i=0; $i < $mnt-1; $i++) { 
        for ($j=0; $j < $mnt-1-$i; $j++) { 
            if($arr[$j]>$arr[$j+1]){
                $temp      = $arr[$j];
                $arr[$j]   = $arr[$j+1];
                $arr[$j+1] = $temp;
            }
            echo $i."——".$j;
            echo "<pre>";
            print_r($arr);
        }
    }
    return $arr;
}
//测试
$arr = [5,2,1,1,3,1,4];
$end = numSort($arr);
echo "<pre>";
print_r($end);

分析：

第1轮：
第1次： Array ( [0] => 2 [1] => 5 [2] => 1 [3] => 1 [4] => 3 [5] => 1 [6] => 4 )

第1轮：
第1次：
Array
(
    [0] => 2
    [1] => 5
    [2] => 1
    [3] => 1
    [4] => 3
    [5] => 1
    [6] => 4
)
第2次：
Array
(
    [0] => 2
    [1] => 1
    [2] => 5
    [3] => 1
    [4] => 3
    [5] => 1
    [6] => 4
)
第3次：
Array
(
    [0] => 2
    [1] => 1
    [2] => 1
    [3] => 5
    [4] => 3
    [5] => 1
    [6] => 4
)
第4次：
Array
(
    [0] => 2
    [1] => 1
    [2] => 1
    [3] => 3
    [4] => 5
    [5] => 1
    [6] => 4
)
第5次：
Array
(
    [0] => 2
    [1] => 1
    [2] => 1
    [3] => 3
    [4] => 1
    [5] => 5
    [6] => 4
)
第6次：
Array
(
    [0] => 2
    [1] => 1
    [2] => 1
    [3] => 3
    [4] => 1
    [5] => 4
    [6] => 5
)
第2轮：
第1次：
Array
(
    [0] => 1
    [1] => 2
    [2] => 1
    [3] => 3
    [4] => 1
    [5] => 4
    [6] => 5
)
第2次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 2
    [3] => 3
    [4] => 1
    [5] => 4
    [6] => 5
)
第3次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 2
    [3] => 3
    [4] => 1
    [5] => 4
    [6] => 5
)
第4次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 2
    [3] => 1
    [4] => 3
    [5] => 4
    [6] => 5
)
第5次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 2
    [3] => 1
    [4] => 3
    [5] => 4
    [6] => 5
)
第3轮：
第1次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 2
    [3] => 1
    [4] => 3
    [5] => 4
    [6] => 5
)
第2次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 2
    [3] => 1
    [4] => 3
    [5] => 4
    [6] => 5
)
第3次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)
第4次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)
第4轮：
第1次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)
第2次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)
第3次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)
第5轮：
第1次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)
第2次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)
第6轮：
第1次：
Array
(
    [0] => 1
    [1] => 1
    [2] => 1
    [3] => 2
    [4] => 3
    [5] => 4
    [6] => 5
)