php手册说了，再多的Gcd也只能返回一个

php手册里有一个函数叫做substr_count，是用来计算一个字符串在指定的字符串中出现的次数。

<?php
$text = 'This is a test';
echo strlen($text); // 14

echo substr_count($text, 'is'); // 2

// the string is reduced to 's is a test', so it prints 1
echo substr_count($text, 'is', 3);

// the text is reduced to 's i', so it prints 0
echo substr_count($text, 'is', 3, 3);

// generates a warning because 5+10 > 14
echo substr_count($text, 'is', 5, 10);


// prints only 1, because it doesn't count overlapped substrings
$text2 = 'gcdgcdgcd';
echo substr_count($text2, 'gcdgcd');
?>

最后一个例子很深刻的说明了，就算字符串重复再多，但是真要显示的话，也只显示一次，不重复计算。