PHP algorithm encounter random thoughts_PHP tutorial-PHP Tutorial-php.cn

PHP algorithm encounter random thoughts_PHP tutorial

WBOY

Release： 2016-07-20 11:15:25

Original

1315 people have browsed it

PHP is really great. Many functions simply implement the functions we want. It is the first choice for rapid project development. To be honest, I think the two best languages for BS program development are PHP And JSP, I have studied Java for a period of time before, and it is indeed very good and complete OOP, but it is too "stupid". Although it has many advantages, it is almost impossible to achieve rapid development. It is too There are many things that need to be followed, and PHP is much better in this regard, but it is precisely because of this that many PHPERs ignore the importance of algorithms. Let’s get back to business today and let’s discuss an algorithm.

Yesterday I encountered a problem when developing a project, which was the combination part. I have studied similar codes and found that they cycled through 7 levels. It made me see stars, not to mention the efficiency. I mentioned it, so I wanted to write a function myself to handle this part. First of all, it must be efficient, and secondly, it must be able to meet my needs. After working on it for a long time, I couldn’t figure it out. The following is an article I posted on CSDN. Help text:

Please help write a function to recombine strings, roughly as follows:

The requirements are as follows:
Type 1: A,B,C
The expected combination is: AB, AC, BC

Type 2: A ,B,C,D (the length of the result can be controlled through parameters, such as the length is 2 or 3)
The expected combination is: AB,AC,AD,BC,BD,CD or ABC,BCD,ACD,ABD
Type 3: A, B, C, D, E (the length of the result can be controlled through parameters, such as the length is 2; 3 or 4) AD,AE,BC,BD,BE,CD,CE,DE or ABC,BCD,CDE,ABD,ABE,ACD,ACE,BDE,BCE,ADE or ABCD,BCDE,ABCE,ACDE,ABDE

The fourth type: A, B, C, D, E, F (the length of the result can be controlled through parameters, such as the length is 2; 3; 4 or 5)
The expected combination is: can be based on the above combination Deduced, no examples will be given here

The above requirements seemed very simple, but when I started writing, I realized that I had no clue at all. I had thought about using recursion, etc., but after much thought, I thought it was not feasible. I searched for a long time and couldn’t find it. I didn't find a similar approach. I only found that someone had written a function in C language. However, when I changed the C language code to PHP and executed it, the effect was very different from the expected one. In the end, I had no choice but to spend 200 precious points on CSDN. Let the experts solve the problem of points. As the saying goes, "There are brave men under heavy rewards." Haha, this sentence is true at all. Soon the PHP version of Buzhu "xuzuning" gave me three answers, sweat!!! Finally, an optimal solution was selected through hundreds of thousands of loop tests. The code is as follows:

It’s a great algorithm. It took me a long time to understand it. Compared with the 7-layer loop written by someone, I don’t know how many times the efficiency has been improved.

	/**
		重新組合Array,例如(2x3;3x3;3x4)
		返回:
			重組後的Array
		參數:
			$arr:要重組的Array
			$len:幾個Array組合到一起
		用法:
			$arr=Array('A1','B2','C3','D4','E5','f');
			$x3=Fun::CombiArray($arr,3);
	/**/
	Public Static Function combiArray($arr,$len){
		$cr = Range(0,$len-1);
		$k = False;
		$total = Count($arr);
		While($cr[0] < $total-($len-1)) {
			$t = Array();
			For($i=0;$i<$len;$i++){$t[]=$arr[$cr[$i]];}
			$r[] = $t;

			For($i=$len-1;$i>=0;$i--) {
				$cr[$i]++;
				For($j=$i;$j<$len-1;$j++){$cr[$j+1] = $cr[$j]+1;}
				IF($cr[$i] < $total-($len-$i-1)){Break;}
			}
		}
		Return $r;
	}

Copy after login

PHP has achieved rapid development, but it has also made programmers stupid. It seems that we need to improve the algorithm. Are there any better books on algorithms? Can you recommend a few to me?

http://www.bkjia.com/PHPjc/440203.html