LeetCode 1736. Latest Time by Replacing Hidden Digits

class Solution {
public:
    string maximumTime(string time) {
        string ans = time;
        if (time[0] == '?') ans[0] = time[1] != '?' && time[1] > '3' ? '1' : '2';
        if (time[1] == '?') ans[1] = ans[0] == '2' ? '3' : '9';
        if (time[3] == '?') ans[3] = '5';
        if (time[4] == '?') ans[4] = '9';
        return ans;
    }
};