11. 最长公共前缀

<?php
class Solution {
    public function longestCommonPrefix($strs) {
        if (!$strs) return '';
        if (count($strs) == 1) return $strs[0];
        $minStr = $strs[0];
        $minStrLen = strlen($minStr);
        foreach ($strs as $k => $str) {
            $len = strlen($str);
            if ($len <= $minStrLen) {
                $minStr = $str;
                $minStrLen = $len;
            }
        }
        $left = 1;
        $right = $minStrLen;
        while ($left <= $right) {
            $mid = floor(($right - $left) / 2) + $left;
            if ($this->_isPrefix($strs, substr($minStr, 0, $mid))) {
                $left = $mid + 1;
            } else {
                $right = $mid - 1;
            }
        }
        return substr($minStr, 0, min($left, $right));
    }
    private function _isPrefix($strs, $prefix) {
        foreach ($strs as $k => $str) {
            if (substr($str, 0, strlen($prefix)) != $prefix) {
                return false;
            }
        }
        return true;
    }
}
$strs = ['flower', 'flow', 'flight'];
// $strs = ['dog', 'cat', 'apple'];
$cls = new Solution();
$ret = $cls->longestCommonPrefix($strs);
print_r($ret);