LeetCode
Master Plan

l, r = 0, len(arr)-1
while l < r:
    if cond: l += 1
    else: r -= 1

l = 0
for r in range(len(s)):
    while invalid: l += 1
    # update answer

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

def bt(start, path):
    if done: res.append(path[:])
    for i in range(start, n):
        path.append(arr[i])
        bt(i+1, path)
        path.pop()

lo, hi = 0, len(arr)-1
while lo <= hi:
    mid = (lo+hi)//2
    if arr[mid] == t: return mid
    elif arr[mid] < t: lo = mid+1
    else: hi = mid-1

parent = list(range(n))
def find(x):
    if parent[x] != x:
        parent[x] = find(parent[x])
    return parent[x]
def union(x,y):
    parent[find(x)] = find(y)

dp = [0] * (n+1)
dp[0] = base_case
for i in range(1, n+1):
    dp[i] = dp[i-1] + ...

class TrieNode:
    def __init__(self):
        self.children = {}
        self.end = False