✅ Top Coding Algorithms You MUST Know for Interviews 💼👨‍💻

🟢 1. Bubble Sort – Sorting Algorithm
👉 Repeatedly compares & swaps adjacent elements to sort the array.

*Python*

def bubble_sort(arr):
    for i in range(len(arr)):
        for j in range(len(arr)-i-1):
            if arr[j] > arr[j+1]:
                arr[j], arr[j+1] = arr[j+1], arr[j]

*C++*

void bubbleSort(int arr[], int n) {
  for(int i=0; i<n-1; i++)
    for(int j=0; j<n-i-1; j++)
      if(arr[j] > arr[j+1])
        swap(arr[j], arr[j+1]);
}

*Java*

void bubbleSort(int[] arr) {
  for(int i = 0; i < arr.length - 1; i++)
    for(int j = 0; j < arr.length - i - 1; j++)
      if(arr[j] > arr[j+1]) {
        int temp = arr[j]; arr[j] = arr[j+1]; arr[j+1] = temp;
      }
}

🟡 2. Binary Search – Searching Algorithm
👉 Efficiently searches a sorted array in O(log n) time.

*Python*

def binary_search(arr, target):
    low, high = 0, len(arr)-1
    while low <= high:
        mid = (low + high) // 2
        if arr[mid] == target: return mid
        elif arr[mid] < target: low = mid + 1
        else: high = mid - 1
    return -1

🟠 3. Recursion – Factorial Example
👉 Function calls itself to solve smaller subproblems.

*C++*

int factorial(int n) {
  if(n == 0) return 1;
  return n * factorial(n - 1);
}

🔵 4. Dynamic Programming – Fibonacci (Bottom-Up)
👉 Stores previous results to avoid repeated work.

*Python*

def fib(n):
    dp = [0, 1]
    for i in range(2, n+1):
        dp.append(dp[i-1] + dp[i-2])
    return dp[n]

🟣 5. Sliding Window – Max Sum Subarray of Size K
👉 Finds max sum in a subarray of fixed length in O(n) time.

*Java*

int maxSum(int[] arr, int k) {
  int sum = 0, max = 0;
  for(int i = 0; i < k; i++) sum += arr[i];
  max = sum;
  for(int i = k; i < arr.length; i++) {
    sum += arr[i] - arr[i - k];
    if(sum > max) max = sum;
  }
  return max;
}

🧠 6. BFS (Breadth-First Search) – Graph Traversal
👉 Explores all neighbors before going deeper.

*Python*

from collections import deque
def bfs(graph, start):
    visited = set([start])
    queue = deque([start])
    while queue:
        node = queue.popleft()
        print(node)
        for neighbor in graph[node]:
             if neighbor not in visited:
                visited.add(neighbor)
                queue.append(neighbor)

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