嵌套循环中的递减影响外循环

Question

尝试显示 1-10 的随机数，每十四（行）七次，每个数字分配不同的背景颜色。我想过使用 2 个嵌套循环，但它没有按预期工作。然后页面加载很长时间："Fatal error: Maximum execution time of 30 seconds exceeded in ..."

我尝试删除内部循环的减量，问题消失了，但我没有得到预期的结果。提前致谢。

$colors = array("grey","white","yellow","red","blue","green","brown","purple","orange","black");
$previousNum = array();
$k = 0;
echo '<table>';
while ($k < 15){
    $k++;
    echo '<tr>';
    for($i = 0; $i < 7; $i++){
        $randNum = mt_rand(1, 10);
        if(!in_array($randNum, $previousNum)){
            echo '<td style="background-color: '.$colors[$randNum-1].'; padding: 10px;">';
            echo $randNum;
            echo '</td>';    
            array_push($previousNum, $randNum);
        }else{
            $i--;
        }
    }
    echo '</tr>';
}

Answer 1

试试这个，希望这对你有帮助。问题是你是，

1. initializing array($previousNum = array();) out of while loop

<?php

$colors = array("grey", "white", "yellow", "red", "blue", "green", "brown", "purple", "orange", "black");
$k = 0;

echo '<table>';

while ($k < 15)
{

    echo '<tr>';

    $previousNum = array();
    for ($i = 0; $i < 7; $i++)
    {
        $randNum = mt_rand(1, 10);
        if (!in_array($randNum, $previousNum))
        {

            echo '<td style="background-color: ' . $colors[$randNum - 1] . '; padding: 10px;">';
            echo $randNum;
            echo '</td>';
            array_push($previousNum, $randNum);
        } 
        else
        {
            $i--;
        }
    }

    $k++;
    echo '</tr>';
}

输出：

Answer 2

您尝试删除减量是正确的。递减将通过运行额外的迭代对性能产生负面影响。您发布的尝试和其他答案没有纠正这个问题，不幸的是它们运行至少 105 (7x15) 个条件语句——这不是最佳实践，也不适合 SO 读者学习。我为您编写了一个新的优化解决方案，没有浪费声明或迭代，并为深色背景添加了白色字体着色。

echo '<table>';
$whitefonts=['black','purple','brown','grey','blue'];  // for visibility
for($k=0; $k<15; ++$k){
    $colors=["grey","white","yellow","red","blue","green","brown","purple","orange","black"];
    echo '<tr>';
    for($i=0; $i<7; ++$i){
        $key=array_rand($colors);
        $color=$colors[$key];
        unset($colors[$key]);
        echo "<td style=\"background-color:$color;";
            if(in_array($color,$whitefonts)){echo "color:white;";}  //  for visibility
        echo "padding:10px;\">",++$key,"</td>";
    }
    echo '</tr>';
}
echo '<table>';

嵌套循环中的递减影响外循环

Decrement in Nested Loop Affects Outer Loop

php

arrays

random

html-table

nested-loops