solves #2437: Number of Valid Clock Times in java

Author: anishLearnsToCode

README.md

@@ -772,7 +772,7 @@
 | 2423 | [Remove Letter To Equalize Frequency](https://leetcode.com/problems/remove-letter-to-equalize-frequency)                                                               |                                                                               [![Java](assets/java.png)](src/RemoveLetterToEqualizeFrequency.java)                                                                               |                                                                                                                                   |
 | 2427 | [Number of Common Factors](https://leetcode.com/problems/number-of-common-factors)                                                                                     |                                                                                    [![Java](assets/java.png)](src/NumberOfCommonFactors.java)                                                                                    |                                                                                                                                   |
 | 2432 | [The Employee That Worked on the Longest Task](https://leetcode.com/problems/the-employee-that-worked-on-the-longest-task)                                             |                                                                            [![Java](assets/java.png)](src/TheEmployeeThatWorkedOnTheLongestTask.java)                                                                            |                                                                                                                                   |
-| 2437 | [Number of Valid Clock Times](https://leetcode.com/problems/number-of-valid-clock-times)                                                                               |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 2437 | [Number of Valid Clock Times](https://leetcode.com/problems/number-of-valid-clock-times)                                                                               |                                                                                   [![Java](assets/java.png)](src/NumberOfValidClockTimes.java)                                                                                   |                                                                                                                                   |
 | 2441 | [Largest Positive Integer That Exists With Its Negative](https://leetcode.com/problems/largest-positive-integer-that-exists-with-its-negative)                         |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2446 | [Determine if Two Events Have Conflict](https://leetcode.com/problems/determine-if-two-events-have-conflict)                                                           |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2451 | [Odd String Difference](https://leetcode.com/problems/odd-string-difference)                                                                                           |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/NumberOfValidClockTimes.java

@@ -0,0 +1,35 @@
+// https://leetcode.com/problems/number-of-valid-clock-times
+// T: O(1)
+// S: O(1)
+
+public class NumberOfValidClockTimes {
+    private static final char QUESTION = '?';
+
+    public int countTime(String time) {
+        return numberOfValidHourStrings(time.substring(0, 2)) * numberOfValidMinuteStrings(time.substring(3));
+    }
+
+    private int numberOfValidMinuteStrings(String mm) {
+        final char first = mm.charAt(0), second = mm.charAt(1);
+
+        if (first == QUESTION && second == QUESTION) return 60;
+        if (first != QUESTION && second != QUESTION) return 1;
+        if (first != QUESTION) return 10;
+        return 6;
+    }
+
+    private int numberOfValidHourStrings(String hh) {
+        final char first = hh.charAt(0), second = hh.charAt(1);
+
+        if (first == QUESTION && second == QUESTION) return 24;
+        if (first != QUESTION && second != QUESTION) return 1;
+
+        if (first != QUESTION) {
+            if (first == '2') return 4;
+            return 10;
+        }
+
+        if (second > '3') return 2;
+        return 3;
+    }
+}