Stacks & Queues — Complete Guide: All Patterns & Problem Index

stack = []  # indices
res = [0] * n
for i in range(n):
    while stack and nums[stack[-1]] < nums[i]:
        res[stack.pop()] = nums[i]
    stack.append(i)

stack = []
for i in range(n):
    while stack and nums[stack[-1]] >= nums[i]:
        stack.pop()
    left[i] = stack[-1] if stack else -1
    stack.append(i)

from collections import deque
queue = deque([start])
visited = {start}
while queue:
    node = queue.popleft()
    for neighbor in get_neighbors(node):
        if neighbor not in visited:
            visited.add(neighbor)
            queue.append(neighbor)

class MinStack:
    def __init__(self): self.stack = []; self.min_stack = []
    def push(self, val):
        self.stack.append(val)
        self.min_stack.append(min(val, self.min_stack[-1] if self.min_stack else val))
    def pop(self): self.stack.pop(); self.min_stack.pop()
    def top(self): return self.stack[-1]
    def getMin(self): return self.min_stack[-1]

from collections import deque
dq = deque()  # stores indices, front is max
res = []
for i in range(n):
    while dq and dq[0] < i - k + 1: dq.popleft()  # remove out-of-window
    while dq and nums[dq[-1]] < nums[i]: dq.pop()  # remove smaller
    dq.append(i)
    if i >= k - 1: res.append(nums[dq[0]])