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# STACK
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2021-10-24 15:18:49 +08:00
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Stack is an ADT (abstract data type) that acts like a list of objects but there is a difference.
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2021-08-23 11:07:33 +08:00
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2021-10-24 15:18:49 +08:00
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Stack works on the principle of _LIFO_ (Last In First Out), it means that the last item added to the stack will be the first item to be removed.
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2021-08-23 11:07:33 +08:00
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2021-10-24 15:18:49 +08:00
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Stack is based on two methods (functions)-
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2021-08-23 11:07:33 +08:00
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2021-10-09 00:17:58 +08:00
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## push(element)
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2021-10-24 15:18:49 +08:00
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It adds "element" to the top of the stack.
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2021-08-23 11:07:33 +08:00
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2021-10-24 15:18:49 +08:00
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For example: If we have `1, 3, 5` in stack, and we call push(9),
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2021-08-23 11:07:33 +08:00
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2021-10-24 15:18:49 +08:00
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`9` will be added to last index of stack -> `1, 3, 5 , 9`.
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2021-08-23 11:07:33 +08:00
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2021-10-09 00:17:58 +08:00
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## peek() or top()
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2021-10-24 15:18:49 +08:00
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It returns element at the top of the stack.
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2021-10-09 00:17:58 +08:00
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2021-10-24 15:18:49 +08:00
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For example: If we have `1, 3, 5` in stack, and we call peek(),
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2021-10-09 00:17:58 +08:00
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2021-10-24 15:18:49 +08:00
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`5` will be returned (without removing it from the stack).
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2021-10-09 00:17:58 +08:00
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## pop()
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2021-10-24 15:18:49 +08:00
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It removes the last element (i.e. top of stack) from stack.
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For example: If we have `1, 3, 5 , 9` in stack, and we call pop(),
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2021-08-23 11:07:33 +08:00
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the function will return `9` and the stack will change to `1, 3, 5`.
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