The narcissus number refers to an n-digit number (n>=3). The sum of the n-th power of the numbers in each digit is equal to itself, and n is its number of digits. (For example: 1^3 5^3 3^3 = 153)
The Narcissus number is also called Armstrong’s number.
There are 4 narcissus numbers with three digits: 153, 370, 371, 407
There are 3 narcissus numbers with four digits : 1634, 8208, 9474
There are three five-digit narcissus numbers: 54748, 92727, 93084
Six-digit narcissus numbers There is one number: 548834
The seven-digit daffodil number has four: 1741725, 4210818, 9800817, 9926315
The eight-digit number There are three daffodil numbers: 24678050, 24678051, 88593477
....
The largest daffodil number has 39 digits ( 115132219018763992565095597973971522401), there are 88 daffodil numbers in the decimal natural numbers.
php Find the number of daffodils
1. Find the number of daffodils by exhaustive method, find 3 ~7-digit narcissus number
39){ return false; } // 保存执行结果 $result = array(); $start = pow(10,$n-1); $end = pow(10, $n); for($i=$start; $i<$end; $i++){ $total = 0; $nums = str_split($i, 1); foreach($nums as $num){ $total += pow($num, $n); } if($total==$i){ array_push($result, $i); } } return $result; } // 获取当前microtime function getMicrotime(){ list($usec, $sec) = explode(' ', microtime()); return (float)$usec + (float)$sec; } // 设定超时时间为3600秒 set_time_limit(3600); // 记录开始运行时间 $start = getMicrotime(); // 执行求出3~7位的水仙花数 for($i=3; $i<=7; $i++){ $result[$i] = implode(',', narcissistic($i)); } // 记录运行结束时间 $end = getMicrotime(); // 输出运行时间 echo 'run time:'.(float)($end - $start); // 打印结果 echo ''; print_r($result); echo ''; ?>Copy after login
Execution result:
run time:82.230147838593 Array ( [3] => 153,370,371,407 [4] => 1634,8208,9474 [5] => 54748,92727,93084 [6] => 548834 [7] => 1741725,4210818,9800817,9926315 )
2. Optimization algorithm Narcissus number, find the narcissus number between 3 and 7 digits
Optimization method: Create a 0-9 N-order correspondence table for pow to reduce the number of calculations
39){ return false; } // 保存执行结果 $result = array(); // n阶pow对应表 $powlist = getPow($n); $start = pow(10,$n-1); $end = pow(10, $n); for($i=$start; $i<$end; $i++){ $total = 0; $nums = str_split($i, 1); foreach($nums as $num){ $total += $powlist[$num]; } if($total==$i){ array_push($result, $i); } } return $result; } // 获取当前microtime function getMicrotime(){ list($usec, $sec) = explode(' ', microtime()); return (float)$usec + (float)$sec; } // 获取n阶pow对应表 function getPow($n){ $powlist = array(); for($i=0; $i<=9; $i++){ array_push($powlist, pow($i,$n)); } return $powlist; } // 设定超时时间为3600秒 set_time_limit(3600); // 记录开始运行时间 $start = getMicrotime(); // 执行求出3~7位的水仙花数 for($i=3; $i<=7; $i++){ $result[$i] = implode(',', narcissistic($i)); } // 记录运行结束时间 $end = getMicrotime(); // 输出运行时间 echo 'run time:'.(float)($end - $start); // 打印结果 echo ''; print_r($result); echo ''; ?>Copy after login
Execution results:
run time:47.354328155518 Array ( [3] => 153,370,371,407 [4] => 1634,8208,9474 [5] => 54748,92727,93084 [6] => 548834 [7] => 1741725,4210818,9800817,9926315 )
Comparing the results, the optimized algorithm reduced the execution time by42%.
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