2437

2437. Number of Valid Clock Times (Easy)

You are given a string of length 5 called time, representing the current time on a digital clock in the format "hh:mm". The earliest possible time is "00:00" and the latest possible time is "23:59".

In the string time, the digits represented by the ? symbol are unknown, and must be replaced with a digit from 0 to 9.

Return an integer answer, the number of valid clock times that can be created by replacing every ? with a digit from 0 to 9.

 

Example 1:

Input: time = "?5:00"
Output: 2
Explanation: We can replace the ? with either a 0 or 1, producing "05:00" or "15:00". Note that we cannot replace it with a 2, since the time "25:00" is invalid. In total, we have two choices.

Example 2:

Input: time = "0?:0?"
Output: 100
Explanation: Each ? can be replaced by any digit from 0 to 9, so we have 100 total choices.

Example 3:

Input: time = "??:??"
Output: 1440
Explanation: There are 24 possible choices for the hours, and 60 possible choices for the minutes. In total, we have 24 * 60 = 1440 choices.

 

Constraints:

• time is a valid string of length 5 in the format "hh:mm".
• "00" <= hh <= "23"
• "00" <= mm <= "59"
• Some of the digits might be replaced with '?' and need to be replaced with digits from 0 to 9.

Companies: Google

Related Topics:
String, Enumeration

Similar Questions:

• Largest Time for Given Digits (Medium)
• Latest Time by Replacing Hidden Digits (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/number-of-valid-clock-times
// Author: github.com/lzl124631x
// Time: O(1)
// Space: O(1)
class Solution {
public:
    int countTime(string s) {
        int ans = 1;
        if (s[0] == '?') {
            if (s[1] == '?') ans *= 24;
            else if (s[1] <= '3') ans *= 3;
            else ans *= 2;
        } else if (s[1] == '?') {
            if (s[0] <= '1') ans *= 10;
            else ans *= 4;
        }
        if (s[3] == '?') {
            if (s[4] == '?') ans *= 60;
            else ans *= 6;
        } else if (s[4] == '?') ans *= 10;
        return ans;
    }
};