leetcode

Author: ayoubzulfiqar

AddDigits/add_digits.dart

@@ -0,0 +1,139 @@
+/*
+
+-* Add Digits *-
+
+Given an integer num, repeatedly add all its digits until the result has only one digit, and return it.
+
+
+
+Example 1:
+
+Input: num = 38
+Output: 2
+Explanation: The process is
+38 --> 3 + 8 --> 11
+11 --> 1 + 1 --> 2
+Since 2 has only one digit, return it.
+Example 2:
+
+Input: num = 0
+Output: 0
+
+
+Constraints:
+
+0 <= num <= 231 - 1
+
+
+Follow up: Could you do it without any loop/recursion in O(1)
+
+
+*/
+// class Solution {
+//   // The problem, widely known as digit root problem, has a congruence formula:
+//   int addDigits(int num) {
+//     return num % 9 == 0 && num > 0 ? 9 : num % 9;
+//   }
+// }
+
+// class B {
+//   int addDigits(int num) {
+//     if (num == 0) return 0;
+//     return num % 9 == 0 ? 9 : num % 9;
+//   }
+// }
+
+// // Recursion
+// class C {
+//   int addDigits(int num) {
+//     String s = num.toString();
+//     int sum = 0;
+//     for (int i = 0; i < s.length; i++) {
+//       sum += s[i].codeUnitAt(0) - '0'.codeUnitAt(0);
+//     }
+//     if (sum > 9) return addDigits(sum);
+//     return sum;
+//   }
+// }
+
+// class D {
+//   int addDigits(int num) {
+//     int x = num;
+//     int sum = 0;
+//     while (x != 0) {
+//       sum = sum + x % 10;
+//       x = x ~/ 10;
+//       if (x == 0 && sum > 9) {
+//         x = sum;
+//         sum = 0;
+//       }
+//     }
+//     return sum;
+//   }
+// }
+
+class A {
+  // The problem, widely known as digit root problem, has a congruence formula:
+  int addDigits(int num) {
+    if (num == 0) return 0;
+    if (num % 9 == 0) return 9;
+    return num % 9;
+  }
+}
+
+class B {
+  int addDigits(int num) {
+    while (num > 9) {
+      int leftNum = num ~/ 10;
+      int rightNum = num % 10;
+      num = leftNum + rightNum;
+    }
+    return num;
+  }
+}
+
+class C {
+  List<int> digits(int num) {
+    List<int> result = [];
+    if (num == 0) {
+      return [0];
+    }
+    while (num != 0) {
+      result.add(num % 10);
+      num ~/= 10;
+    }
+    return result;
+  }
+
+  int addDigits(int num) {
+    var digitList = digits(num);
+    while (digitList.length > 1) {
+      int sum = 0;
+      for (int d in digitList) {
+        sum += d;
+      }
+      digitList = digits(sum);
+    }
+    return digitList[0];
+  }
+}
+
+class D {
+  int addDigits(int num) {
+    int sum = 0;
+    if (num == 0) {
+      return 0;
+    }
+
+    while (num > 0) {
+      if ((sum + num % 10) > 9) {
+        sum = 1 + (sum + num % 10) % 10;
+      } else
+        sum += num % 10;
+
+      num = num ~/ 10;
+    }
+
+    return sum;
+  }
+}

AddDigits/add_digits.go

@@ -0,0 +1,11 @@
+package main
+
+func addDigits(num int) int {
+	if num == 0 {
+		return 0
+	}
+	if num%9 == 0 {
+		return 9
+	}
+	return num % 9
+}

AddDigits/add_digits.md

@@ -0,0 +1,100 @@
+# 🔥 Add Digits 🔥 || 5 Solutions || Simple Fast and Easy
+
+## The problem, widely known as digit root problem, has a congruence formula
+
+## Solution - 1 Mathematical Congruence Formula
+
+```dart
+class Solution {
+  int addDigits(int num) {
+    if (num == 0) return 0;
+    if (num % 9 == 0) return 9;
+    return num % 9;
+  }
+}
+```
+
+## Solution - 2 Two Pointers
+
+```dart
+class Solution {
+  int addDigits(int num) {
+    while (num > 9) {
+      int leftNum = num ~/ 10;
+      int rightNum = num % 10;
+      num = leftNum + rightNum;
+    }
+    return num;
+  }
+}
+```
+
+## Solution - 3 Using Array
+
+```dart
+class Solution {
+  List<int> digits(int num) {
+    List<int> result = [];
+    if (num == 0) {
+      return [0];
+    }
+    while (num != 0) {
+      result.add(num % 10);
+      num ~/= 10;
+    }
+    return result;
+  }
+
+  int addDigits(int num) {
+    var digitList = digits(num);
+    while (digitList.length > 1) {
+      int sum = 0;
+      for (int d in digitList) {
+        sum += d;
+      }
+      digitList = digits(sum);
+    }
+    return digitList[0];
+  }
+}
+```
+
+## Solution - 4
+
+```dart
+class Solution {
+  int addDigits(int num) {
+    int sum = 0;
+    if (num == 0) {
+      return 0;
+    }
+
+    while (num > 0) {
+      if ((sum + num % 10) > 9) {
+        sum = 1 + (sum + num % 10) % 10;
+      } else
+        sum += num % 10;
+
+      num = num ~/ 10;
+    }
+
+    return sum;
+  }
+}
+```
+
+## Solution - 5 Recursion
+
+```dart
+class Solution {
+  int addDigits(int num) {
+    String s = num.toString();
+    int sum = 0;
+    for (int i = 0; i < s.length; i++) {
+      sum += s[i].codeUnitAt(0) - '0'.codeUnitAt(0);
+    }
+    if (sum > 9) return addDigits(sum);
+    return sum;
+  }
+}
+```

README.md

@@ -97,6 +97,7 @@ This repo contain leetcode solution using DART and GO programming language. Most
 - [Meeting Rooms](MeetingRooms/meeting_rooms.dart)
 - [Delete the Middle Node of a Linked List](DeleteTheMiddleNodeOfALinkedList/delete_the_middle_node_of_a_linked_list.dart)
 - [String Compression II](StringCompression-II/string_compression_II.dart)
+- [Add Digits](AddDigits/add_digits.dart)
 
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