Solve Ransom Note Problem Easily with Leetcode

Table of Contents

1. Introduction
2. Problem Description
3. Examples
4. Logic to Solve the Problem
5. Step-by-Step Implementation
6. Complexity Analysis
7. Conclusion

Article

Introduction

In this article, we will discuss the "Ransom Note" problem from LeetCode. The problem is about checking whether a given ransom note can be constructed using the letters from a magazine string.

Problem Description

The problem provides two strings: the ransom note and the magazine. Our task is to determine whether the ransom note can be built using the letters from the magazine. Each letter in the magazine string can only be used once in the ransom note.

Examples

Let's take a few examples to understand the problem better:

1. Example 1:

   • Ransom Note: "a"
   • Magazine: "b"
   • Output: False Explanation: We need to build "a" from the magazine, but "a" is not present inside the magazine. Thus, we return False.

2. Example 2:

   • Ransom Note: "aa"
   • Magazine: "aab"
   • Output: False Explanation: We need to build two "a"s from the string "aab". However, there is only one "a" available in the magazine, so we cannot build the ransom note. Thus, we return False.

3. Example 3:

   • Ransom Note: "aa"
   • Magazine: "aabb"
   • Output: True Explanation: There are two "a"s and two "b"s present inside the magazine, so we can build the ransom note. Thus, we return True.

Logic to Solve the Problem

To solve this problem, we can follow the steps below:

1. Create a hash map for the magazine string. The keys in the hash map will represent the characters present in the magazine, and the values will represent the frequency of each character.
2. Iterate through the ransom note string from left to right, checking each character present in the string.
3. In each iteration, check if the current character is present inside the map and if its frequency is greater than zero.
4. If both conditions pass, increment a count variable and decrement the frequency of that character in the map by one.
5. After iterating through the entire ransom note string, check if the count variable is equal to the length of the ransom note string. If they are equal, return True; otherwise, return False.

Step-by-Step Implementation

Let's implement the logic step-by-step.

1. Create a hash map for the magazine string.
2. Iterate through the magazine string and update the frequency of each character in the hash map.
3. Iterate through the ransom note string and check if each character is present in the hash map with a positive frequency.
4. If all characters are present and have a positive frequency, return True; otherwise, return False.

Complexity Analysis

The time complexity of this approach is O(N), where N is the length of the ransom note string. This is because we iterate through the ransom note and magazine strings only once. The space complexity is also O(N), as we use a hash map to store the frequency of characters in the magazine string.

Conclusion

In this article, we discussed the "Ransom Note" problem from LeetCode. We explained the problem statement, provided examples, and discussed the logic and step-by-step implementation to solve the problem. We also analyzed the time and space complexity of the solution. By following the approach discussed, you should be able to solve this problem efficiently.