stack 是 first-in-last-out 或者是 last-in-first-out
push的功能是把一个东西(例如一个数字)放进stack里面
pop的功能是把最后的东西移除
(一开始)空的stack:
| |
| |
| |
——
push "A":
| |
| |
| A |
——
push "B":
| |
| B |
| A |
——
pop过后:
| |
| |
| A |
——
push "C":
| |
| C |
| A |
——
push "D":
| D |
| C |
| A |
——
pop过后:
| |
| C |
| A |
——
pop过后:
| |
| |
| A |
——
pop过后:
| |
| |
| |
——