Introduction: Efficient algorithms are the backbone of modern software development. In this blog post, we will explore the sliding window technique—an algorithmic approach that can dramatically improve efficiency in certain scenarios. We will delve into how this technique works, and its efficiency benefits, and showcase a real-world use case in a banking application.

Understanding the Sliding Window Technique: The sliding window technique involves maintaining a "window" of elements within a data structure and iteratively sliding the window to solve a specific problem efficiently. By optimizing the way we process data, we can often achieve better time complexity compared to brute-force approaches.

Efficiency Benefits:

1. Reduced Computation: The sliding window technique avoids unnecessary recomputations by reusing previously computed results within the window. This leads to improved time complexity and faster execution.

2. Linear Complexity: In many cases, the sliding window technique allows us to solve problems with linear time complexity (O(n)), which is far more efficient than quadratic or exponential complexity.

Use Case 1: Banking Application: Consider a banking application that needs to identify the longest consecutive sequence of transactions above a certain threshold amount. The sliding window technique is a perfect fit for this scenario. By maintaining a window of transaction amounts and sliding it through the data, we can efficiently identify the longest sequence without checking every possible subarray.

Let's look at a JavaScript implementation of the sliding window technique for this use case:

function findLongestSequence(transactions, threshold) {
  let maxLength = 0;
  let currentLength = 0;

  for (let i = 0; i < transactions.length; i++) {
    if (transactions[i] > threshold) {
      currentLength++;
    } else {
      maxLength = Math.max(maxLength, currentLength);
      currentLength = 0;
    }
  }

  return Math.max(maxLength, currentLength);
}

// Example usage:
const transactions = [120, 140, 200, 80, 100, 250, 300, 320, 200, 180];
const threshold = 150;
const longestSequence = findLongestSequence(transactions, threshold);
console.log(`Longest sequence above ${threshold}: ${longestSequence}`);

In this example, we define the findLongestSequence function that takes an array of transactions and a threshold amount. The function iterates over the transactions, maintaining the current length of consecutive amounts above the threshold. When a transaction falls below the threshold, the current length is compared with the maximum length encountered so far. Finally, the function returns the longest sequence length.

Use Case 2: Fraud Detection - Anomaly Detection Detecting anomalies and potential fraud in banking transactions is critical. The sliding window technique can be used to identify unusual patterns in transaction amounts.

function detectAnomalies(transactions, windowSize, threshold) {
  const anomalies = [];

  for (let i = 0; i < transactions.length; i++) {
    if (i >= windowSize) {
      const window = transactions.slice(i - windowSize, i);
      const average = window.reduce((sum, amount) => sum + amount, 0) / windowSize;

      if (transactions[i] > threshold * average) {
        anomalies.push({ transaction: transactions[i], index: i });
      }
    }
  }

  return anomalies;
}

// Example usage:
const transactionAmounts = [100, 150, 200, 120, 180, 900, 120, 250, 300, 80];
const windowSize = 5;
const anomalyThreshold = 2;
const detectedAnomalies = detectAnomalies(transactionAmounts, windowSize, anomalyThreshold);
console.log('Detected Anomalies:', detectedAnomalies);

In this example, we detect anomalies in transaction amounts by comparing each transaction to the average of the previous window. If a transaction exceeds a certain threshold (e.g., twice the average), it is flagged as an anomaly. By using a sliding window, we can efficiently analyze transaction patterns and identify potential fraud.

Another example with strings: Longest Substring with K Distinct Characters Given a string, you can use the sliding window technique to find the length of the longest substring that contains at most K distinct characters.

function findLongestSubstringWithKDistinct(str, k) {
  let longestLength = 0;
  let start = 0;
  const charMap = new Map();

  for (let end = 0; end < str.length; end++) {
    const currentChar = str[end];
    charMap.set(currentChar, (charMap.get(currentChar) || 0) + 1);

    while (charMap.size > k) {
      const leftChar = str[start];
      charMap.set(leftChar, charMap.get(leftChar) - 1);
      if (charMap.get(leftChar) === 0) {
        charMap.delete(leftChar);
      }
      start++;
    }

    longestLength = Math.max(longestLength, end - start + 1);
  }

  return longestLength;
}

// Example usage:
const inputString = 'aabacbebebe';
const k = 3;
const longestLength = findLongestSubstringWithKDistinct(inputString, k);
console.log(`Length of the longest substring with ${k} distinct characters: ${longestLength}`);

Thanks for reading so far. Happy Learning !!