1796. Second Largest Digit in a String

Given an alphanumeric string s, return the second largest numerical digit that appears in s, or -1 if it does not exist.

An alphanumeric string is a string consisting of lowercase English letters and digits.

 

Example 1:

Input: s = "dfa12321afd"
Output: 2
Explanation: The digits that appear in s are [1, 2, 3]. The second largest digit is 2.
Example 2:

Input: s = "abc1111"
Output: -1
Explanation: The digits that appear in s are [1]. There is no second largest digit. 
 

Constraints:

1 <= s.length <= 500
s consists of only lowercase English letters and/or digits.

这题需要从一个字符串中找出第二大的整数。我们可以声明两个变量，分别是最大的，第二大的整数。

扫描的时候，假设当前数值比最大的还大，则将最大的数放入第二大的数里，当前放入最大；反之当比最大的小的时候，我们也需要比较和第二大的关系，假设大于第二大，则还是需要赋值的。

class Solution {
public:
    int secondHighest(string s) {
        int n1 = -1, n2 = -1;
        for (auto v : s) {
            if (v < '0' || v > '9') {
                continue;
            }
            if (v - '0' > n2) {
                n1 = n2;
                n2 = v - '0';
            } else if (v - '0' < n2 && v - '0' > n1) {
                n1 = v - '0';
            }
        }
        return n1;
    }
};