String to Integer (atoi)

原题链接-M

Example
Example 1:

Input: "42"
Output: 42
Example 2:

Input: " -42"
Output: -42

Example 3:

Input: "4193 with words"
Output: 4193

Example 4:

Input: "words and 987"
Output: 0

Example 5:

Input: "-91283472332"
Output: -2147483648

时间复杂度: O(N)- 空间复杂度: O(1)

print_r(test(' 123fdfa'));

function test($str) {
    $str = trim($str);
    if (mb_strlen($str) == 0) {
        return 0;
    }
    
    $position = true;
    if ($str[0] == '+' || $str[0] == '-') {
        if ($str[0] == '-') {
            $position = false;
        }
        $str = substr($str,1,mb_strlen($str)-1);
    } elseif ($str[0] < '0' || $str[0] > '9') {
        return 0;
    }
    
    $rest = 0;
    
    for ($i = 0; $i < mb_strlen($str); $i++) {
        $char = $str[$i];
        if ($char < '0' || $char > '9') {
            break;
        }
        
        if ($char >= 0 || $char <= 9) {
            $rest = $rest*10 + intval($char);
        }
    }
    
    if ($position==false) {
       $rest = 0-$rest;
    }
    return $rest;
}