Foundations #06 - Stacks & Queues

Track: Foundations

Do dabbe jinme cheez rakhne ka tareeka same hai, bas nikaalne ka order ulta-pulta, aur unhi dabbon se aage do interview patterns nikalte hain.

Before you start. Array yaad karo: dabbon ki ek seedhi row, har dabbe ka apna number, jispe seedhe pahunchna sasta hota hai - Foundations #01 - Complexity (Big-O ka poora naksha) mein yehi “ek baar chhuo, seedhe pahuncho” wala hisaab dekha tha. Yeh lesson usi row ke upar do niyam rakhta hai - cheez andar kaise jaati hai, aur sabse zaroori, kaunsi cheez sabse pehle bahar aati hai.

The idea in 30 seconds

Stack = LIFO: sabse aakhri andar gayi cheez sabse pehle bahar aati hai; push daalta hai, pop nikaalta hai.
Queue = FIFO: sabse pehle andar gayi cheez sabse pehle bahar aati hai; peeche judti hai, aage se nikalti hai.
Nesting, matching ya undo maangne wale sawaal stack maangte hain; order-preserve ya level-by-level maangne wale queue - sawaal padhte hi yeh sawaal khud se poochho.
JavaScript ka array khud stack ki tarah tez hai, par queue ki tarah nahi - agla hissa dikhayega kyun.
Ek chhoti tarkeeb ke saath stack “agla bada/garam” jaise sawaal ka jawab bhi de deta hai - second read mein.
Function calls khud isi chhupe dabbe mein jamti hain, isliye function ka khud ko bulaana (recursion) aur apna banaya stack ek hi kaam alag tareeke se karte hain - dono aage second read mein milenge.

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