Add ransom note

Author: onixlas

hashmap/383_ransom_note/README.md

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+# Ransom Note
+
+## Problem Description
+
+Given two strings `ransomNote` and `magazine`, return `true` if `ransomNote` can be constructed by using the letters from `magazine` and `false` otherwise.
+
+Each letter in `magazine` can only be used once in `ransomNote`.
+
+**Example 1:**
+
+Input: `ransomNote = "a"`, `magazine = "b"`
+Output: `false`
+
+**Example 2:**
+
+Input: `ransomNote = "aa"`, `magazine = "ab"`
+Output: `false`
+
+**Example 3:**
+
+Input: `ransomNote = "aa"`, `magazine = "aab"`
+Output: ``true`
+
+**Constraints:**
+
+* `1 <= ransomNote.length, magazine.length <= 105`
+* `ransomNote` and `magazine` consist of lowercase English letters.
+
+## Solution
+
+```python
+def can_construct(self, ransom_note: str, magazine: str) -> bool:
+    """
+    Check if the `ransom_note` can be constructed from the letters of `magazine`.
+
+    Each letter in `magazine` can only be used once in `ransom_note`. The function determines
+    if there are enough characters in `magazine` to form the `ransom_note` (considering character counts).
+
+    :param self: Instance reference (used if this is a method in a class).
+    :param ransom_note: String that needs to be constructed.
+    :param magazine: String containing available characters.
+    :return: True if `ransom_note` can be constructed from `magazine`, False otherwise.
+    """
+    hashmap = {}
+    for character in magazine:
+        if character not in hashmap:
+            hashmap[character] = 1
+        else:
+            hashmap[character] += 1
+    for character in ransom_note:
+        if character not in hashmap or hashmap[character] == 0:
+            return False
+        else:
+            hashmap[character] -= 1
+    return True
+```
+
+* **Time Complexity:** $O(m + n)$
+* **Space Complexity:** $O(1)$
+
+## Explanation of the Solution
+
+Step-by-Step Breakdown:
+
+1. Count Characters in magazine:
+
+    * A hashmap (dictionary) is used to store the count of each character in magazine.
+    * For each character in magazine:
+      * If the character is not in the hashmap, add it with a count of 1.
+      * If the character exists, increment its count by 1.
+
+    **Example:**
+    `magazine = "aab"` → `hashmap = {'a': 2, 'b': 1}`
+
+2. Check Characters in ransom_note:
+   * For each character in ransom_note:
+        * If the character is missing in the hashmap or its count is 0, return False (cannot construct the note).
+        * Otherwise, decrement the count of that character in the hashmap (to mark it as "used").
+3. Return True if All Checks Pass:
+   * If the loop completes without issues, ransom_note can be constructed → Return True.

hashmap/383_ransom_note/solution.py

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+def can_construct(self, ransom_note: str, magazine: str) -> bool:
+    """
+    Check if the `ransom_note` can be constructed from the letters of `magazine`.
+
+    Each letter in `magazine` can only be used once in `ransom_note`. The function determines
+    if there are enough characters in `magazine` to form the `ransom_note` (considering character counts).
+
+    :param self: Instance reference (used if this is a method in a class).
+    :param ransom_note: String that needs to be constructed.
+    :param magazine: String containing available characters.
+    :return: True if `ransom_note` can be constructed from `magazine`, False otherwise.
+    """
+    hashmap = {}
+    for character in magazine:
+        if character not in hashmap:
+            hashmap[character] = 1
+        else:
+            hashmap[character] += 1
+    for character in ransom_note:
+        if character not in hashmap or hashmap[character] == 0:
+            return False
+        else:
+            hashmap[character] -= 1
+    return True
+
+
+
+assert can_construct(ransom_note='a', magazine='b') == False, 'Test 1 Failed'
+assert can_construct(ransom_note='aa', magazine='ab') == False, 'Test 2 Failed'
+assert can_construct(ransom_note='aa', magazine='aab') == True, 'Test 3 Failed'