🌱 DSA (Beginner) · Essential Data Structures · cozy lesson
Stack & Queue
10 min · 1 min read · no scary math, promise
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def valid(s):
st, m = [], {')':'(',']':'[','}':'{'}
for ch in s:
if ch in '([{': st.append(ch)
else:
if not st or st.pop()!=m[ch]: return False
return not st
Queue = FIFO (BFS). Monotonic stack next: keep increasing to find next greater in O(n).
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Correct answers earn XP (once each).
1. Stack is…
2. Valid parens via?
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