L&T (Larsen & Toubro) Interview Preparation

def rotate(arr, k):
    k = k % len(arr)
    arr[:] = arr[-k:] + arr[:-k]

def trap(height):
    if not height: return 0
    left, right = 0, len(height)-1
    max_left = max_right = water = 0
    while left < right:
        if height[left] < height[right]:
            max_left = max(max_left, height[left])
            water += max_left - height[left]
            left += 1
        else:
            max_right = max(max_right, height[right])
            water += max_right - height[right]
            right -= 1
    return water

import heapq
def mergeKLists(lists):
    heap = [(head.val, i, head) for i, head in enumerate(lists) if head]
    heapq.heapify(heap)
    dummy = Node(0)
    curr = dummy
    while heap:
        val, i, node = heapq.heappop(heap)
        curr.next = node
        curr = curr.next
        if node.next:
            heapq.heappush(heap, (node.next.val, i, node.next))
    return dummy.next