Encountered an interesting problem, and calculated the efficiency of the two methods, and found that if all the combinations are exhausted, there are as many as 1,000,000 permutations ~ so it is simplified to 600 times. So, one of your conditions, or an operation, may be thousands of times more efficient!
<?php
header("Content-Type:text/html;charset=utf-8");
//百钱买小鸡
/* 公鸡5文钱1只，母鸡三文钱一只，小鸡一文钱三只。 现在用100文钱共买了100只鸡， 问这100只鸡中，公鸡，母鸡，小鸡各是多少只？ */ $start = microtime(true); //写法一 穷举所有排列：计算1000000次。 for($g = 1; $g <= 100; $g++){ for($m = 1; $m <= 100; $m++){ for($x = 1; $x <= 100; $x++){ if($g+$m+$x == 100 && $g*5+$m*3+$x/3==100){ echo "公，母，雏，分别为：".$g." ".$m." ".$x."<br />"; } //计算排列组合次数 if($g == 100 && $m == 100 && $x == 100){ echo "排列次数为：".$g*$m*$x; } } } } echo "<br />"; $end = microtime(true); echo "函数执行时间为：".($end - $start);//计算函数运行时间。 echo "<br />"; //写法二：简化组合. $start = microtime(true); for($g = 1; $g < 20; $g++){ for($m = 1; $m <= 33; $m++){ $x = 100 - $g - $m; if($g+$m+$x == 100 && $g*5+$m*3+$x/3==100){ echo "公，母，雏，分别为：".$g." ".$m." ".$x."<br />"; } //计算排列组合次数 if($g == 19 && $m == 33){ echo "排列次数为：".$g*$m; } } } echo "<br />"; $end = microtime(true); echo "函数执行时间为：".($end - $start);//计算函数运行时间。 echo "<br />"; ?>- 1
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Output result 1:
male, female, chick, respectively: 4 18 78
male, female, chick, respectively: 8 11 81
male, female, chick, respectively: 12 4 84
The number of permutations is: 1000000 The
execution time of the function is: 0.10584402084351
Let's take a look at the second set of algorithms ~ a thousand times worse ~ although it is milliseconds.
Output result 2:
male, female, chick, respectively: 4 18 78
male, female, chick, respectively: 8 11 81
male, female, chick, respectively: 12 4 84
The number of permutations is: 627 The
execution time of the function is: 0.00016307830810547