Kiganja ni nini na kinatumika kwa nini?

Question

Accepted Answer

**Kiganja** ni mkusanyiko wa **LIFO** (Last-In, First-Out) — kipengele kilichoingizwa mwisho ndilo litakachochukuliwa kwanza. Unagusa tu **juu** ya kiganja.

## Operesheni

```text
push(3)   push(7)   pop()->7   peek()->3
 [ 3 ]     [ 7 ]      [ 3 ]      [ 3 ]
           [ 3 ]                 top
            top
```

## Mfano

```python
stack = []
stack.append('a')   # push
stack.append('b')   # push
top = stack[-1]     # peek -> 'b'
stack.pop()         # pop  -> 'b'
```

Operesheni zote ni **O(1)** wakati zimesisimuliwa na safu inayobadilika au orodha iliyounganishwa.

| Operesheni | Wakati |
|---|---|
| push | O(1) |
| pop | O(1) |
| peek | O(1) |

## Matumizi ya kawaida

- **Function call stack** — inafuatilia simu zinazotendeka na anuwai za ndani.
- **Undo/redo** — ingiza kila hatua; chukua kutochelewa.
- **Tathmini ya usemi / uchambuzi** — kulinganisha mabano, kubadilisha infix kuwa postfix.
- **Kurudi nyuma & DFS** — kumbuka mahali pa kurudi.

## Kwa nini ni muhimu

Kiganja kinaiga "fanya kitu cha hivi karibuni kwanza," ambacho kinaonekana kila mahali kutoka kwa recursion hadi kwa kitufe cha kurudi nyuma cha kivinjari.

Kutambua muundo wa LIFO mara moja kunapendekeza kiganja, mara nyingi kubadilisha tatizo linalochanganyikiwa kuwa safu nzuri za push/pop.