Learning Stack data structure [Java]

Stack:

Stack stores elements of the same data type.

We can insert, and remove elements in the stack in the Last In First Out policy (LIFO)

Declaration

Stack<Type> variable_name = new Stack<>();

Stack<Integer> stack = new Stack<>();

Methods used in Stack:

stack_name . push() – insert element into a stack

stack_name . peek() – checks the topmost element in the stack

stack_name . pop() – removes the topmost element in the stack

stack_name . size() – returns the number of elements in stack

stack_name . empty() – returns true / false. if stack is empty, it returns true. if stack is not empty it retuns false

stack_name . clear() – clears the stack

stack_name . contains(value) –  returns true if the value we check is there in stack or else it returns false
stack_name remove(index) – removes the value in given index

stack_name . search(value) – searches the value in stack and returns us the index of the value if present.

Iterating stack:

We can go through the stack elements in two ways.

1. Popping the elements

We can pop the stack elements one by one and go through all the elements.

2. For each loop

We can go through the stack by a for loop as below

for(String s : stack_name)

{

//Stack will be iterated from bottom to top direction in this way

}

How to identify if that problem can be solved using a stack

1. when we want to evaluate brackets, expressions in certain order we can use stacks.

2. When we wanted to use backspace character in keyboard or any similar sitautions, we can use stacks

3. When we want to delete or remove the last elements we can use stack.

4. When we want to backtrack to something and then again to move forward direction multiple times we can use stack.

5. We can use stack to find some peak elements (assuming the value plotted something like graph) we can use stacks

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