14. 最长公共前缀

题意：

解题思路：

思路：
    1. 以数组中第一个字符串做为比较对象，循环截取第1个字符串的第i个字符跟后面n个字符串的第i个字符做比较；
    2. 当i大于后面字符串长度时，或者字符串不等时，终止；

PHP代码实现：

class Solution {
    /**
     * @param String[] $strs
     * @return String
     */
    function longestCommonPrefix1($strs) {
        if ($strs == null || count($strs) == 0) return "";
        if (count($strs) == 1) return $strs[0];
        $first = $strs[0];
        for ($i = 0; $i < strlen($first); ++$i) {
            $c = $first[$i];
            for ($j = 1; $j < count($strs); ++$j) {
                if ($i >= strlen($strs[$j]) || $strs[$j][$i] != $c) {
                    return substr($first, 0, $i);
                }
            }
        }
        return $first;
    }
    function longestCommonPrefix($strs) {
        return $this->longestCommonPrefix1($strs);
        if (!$strs) return '';
        if (count($strs) == 1) return $strs[0];
        $min = strlen($strs[0]);
        $key = 0;
        foreach ($strs as $k => $str) {
            if (strlen($str) <= $min) {
                $key = $k;
                $min = strlen($str);
            }
        }
        $minStr = $strs[$key];
        unset($strs[$key]);
        $left = 1;
        $right = strlen($minStr);
        while ($left <= $right) {
            $mid = $left + floor(($right - $left) / 2);
            if ($this->isPrefix($strs, substr($minStr, 0, $mid))) {
                $left = $mid + 1;
            } else {
                $right = $mid - 1;
            }
        }
        return substr($minStr, 0, min($left, $right));
    }
    function isPrefix($strs, $prefix) {
        foreach ($strs as $s) {
            if (substr($s, 0, strlen($prefix)) != $prefix) {
                return false;
            }
        }
        return true;
    }
}

GO代码实现：

func longestCommonPrefix(strs []string) string {
    if len(strs) == 0 {
        return ""
    }
    for i := 0; i < len(strs[0]); i++ {
        for j := 1; j < len(strs); j++ {
            if i >= len(strs[j]) || strs[j][i] != strs[0][i] {
                return strs[0][:i]
            }
        }
    }
    return strs[0]
}