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2437. Number of Valid Clock Times

Description

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.

Solutions

Solution 1: Enumeration

We can directly enumerate all times from $00:00$ to $23:59$, then judge whether each time is valid, if so, increment the answer.

After the enumeration ends, return the answer.

The time complexity is $O(24 \times 60)$, and the space complexity is $O(1)$.

Solution 2: Optimized Enumeration

We can separately enumerate hours and minutes, count how many hours and minutes meet the condition, and then multiply them together.

The time complexity is $O(24 + 60)$, and the space complexity is $O(1)$.

  • class Solution {
    public int countTime(String time) {
        int ans = 0;
        for (int h = 0; h < 24; ++h) {
            for (int m = 0; m < 60; ++m) {
                String s = String.format("%02d:%02d", h, m);
                int ok = 1;
                for (int i = 0; i < 5; ++i) {
                    if (s.charAt(i) != time.charAt(i) && time.charAt(i) != '?') {
                        ok = 0;
                        break;
                    }
                }
                ans += ok;
            }
        }
        return ans;
    }
}

  • class Solution {
public:
    int countTime(string time) {
        int ans = 0;
        for (int h = 0; h < 24; ++h) {
            for (int m = 0; m < 60; ++m) {
                char s[20];
                sprintf(s, "%02d:%02d", h, m);
                int ok = 1;
                for (int i = 0; i < 5; ++i) {
                    if (s[i] != time[i] && time[i] != '?') {
                        ok = 0;
                        break;
                    }
                }
                ans += ok;
            }
        }
        return ans;
    }
};

  • class Solution:
    def countTime(self, time: str) -> int:
        def check(s: str, t: str) -> bool:
            return all(a == b or b == '?' for a, b in zip(s, t))

        return sum(
            check(f'{h:02d}:{m:02d}', time) for h in range(24) for m in range(60)
        )


  • func countTime(time string) int {
	ans := 0
	for h := 0; h < 24; h++ {
		for m := 0; m < 60; m++ {
			s := fmt.Sprintf("%02d:%02d", h, m)
			ok := 1
			for i := 0; i < 5; i++ {
				if s[i] != time[i] && time[i] != '?' {
					ok = 0
					break
				}
			}
			ans += ok
		}
	}
	return ans
}

  • function countTime(time: string): number {
    let ans = 0;
    for (let h = 0; h < 24; ++h) {
        for (let m = 0; m < 60; ++m) {
            const s = `${h}`.padStart(2, '0') + ':' + `${m}`.padStart(2, '0');
            let ok = 1;
            for (let i = 0; i < 5; ++i) {
                if (s[i] !== time[i] && time[i] !== '?') {
                    ok = 0;
                    break;
                }
            }
            ans += ok;
        }
    }
    return ans;
}


  • impl Solution {
    pub fn count_time(time: String) -> i32 {
        let mut ans = 0;

        for i in 0..24 {
            for j in 0..60 {
                let mut ok = true;
                let t = format!("{:02}:{:02}", i, j);

                for (k, ch) in time.chars().enumerate() {
                    if ch != '?' && ch != t.chars().nth(k).unwrap() {
                        ok = false;
                    }
                }

                if ok {
                    ans += 1;
                }
            }
        }

        ans
    }
}

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