PHP实现四种排序-冒泡排序

程序=算法+数据结构，作为一个PHP程序员，需要掌握一下。

代码实现：

/**
*    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;
			}
		}
	}
	return $arr;
}
//测试
$arr = [5,2,1,1,3,1,4];
$end = numSort($arr);
echo "<pre>";
print_r($end);

过程分析：

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 )

结论：

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）