プログラマ脳を鍛える数学パズルQ02

q02.php

<?php

error_reporting(0);// division by zeroのワーニング回避
$expression = array("+","-","*","/","");

for($num = 1000; $num <= 9999;$num++){
    foreach($expression as $i){
        // 1つめの間
        foreach($expression as $j){
            // 2つ目の間
            foreach($expression as $k){
                // 3つめの間
                $tmp_expression = substr($num,0,1). $i. substr($num, 1,1). $j. substr($num,2,1). $k. substr($num, 3,1);
                $calc_res = eval("return {$tmp_expression};");

                if($calc_res == strrev($num) && strlen($calc_res) >= 4 && (!empty($i) || !empty($j) || !empty($k))){
                    print("base=".$num.",strrev = ".strrev($num).", calc_res = {$calc_res}, expression={$tmp_expression}\n");
                }
            }
        }
    }
}

結果

$ php -f q02.php
base=5931,strrev = 1395, calc_res = 1395, expression=5_9_31