Stacks And Queues

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Stack Implementation Details

C :
Stack declaration : :
    int A[MAX_SIZE]; // create a integer array of maximum expected size for the stack
    int *A = (int *) malloc(1000 * sizeof(int)); // or malloc it.
    int size = 0; // Also keep track of the current size
Push
    A[size++] = newElement; // Put the new Element on the end of the array. O(1).
Pop
    size--; // Simply reduce the size. O(1)
isEmpty
    return (size == 0); // Check if size is 0. O(1)
Size
    return size; // 'size' tracks the current size of the stack. 
Top
    A[size - 1]
C++ :

C style array stack works in C++ as well. However, C++ provides a library implementation of stack as well.

Stack declaration : :
    stack<int> A; // declares an empty stack. 
Push
    A.push(newElement); // Pushes a new element. O(1)
Pop
    A.pop(); // O(1) pop
isEmpty
    A.empty() // O(1) 
Size
    A.size(); // O(1) 
Top
    A.top(); // O(1). Gives the top element. 
JAVA :

Java has a stack similar to C++.

Stack declaration : :
    Stack<Integer> A = new Stack<Integer>(); 
Push
    A.push(new Integer(newElement)); // Pushes a new element. O(1)
Pop
    A.pop(); // O(1) pop
isEmpty
    A.empty() // O(1) 
Size
    A.size(); // O(1) 
Top
    A.peek(); // O(1). Gives the top element. 
PYTHON :

We can use list as a stack in python. Very similar to how we do it in C.

Stack declaration : :
    A = [] # declares an empty stack. O(1)
Push
    A.append(newElement) # Put the new Element on the end of the array. O(1).
Pop
    A.pop()  # removes the last element. O(1)
isEmpty
    return (len(A) == 0); # Check if size is 0. O(1)
Size
    return len(A); # O(1)  
Top
    A[-1] # O(1)




Walkthrough examples :

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Stacks And Queues Problems

Stack simple
Problem Score Companies Time Status
Balanced Parantheses! 200 15:59
Simplify Directory Path 250
54:00
Redundant Braces 300 42:41
Min Stack 400 43:31
Cleverstack
Problem Score Companies Time Status
MAXSPPROD 200
88:22
Nearest Smaller Element 350 41:37
Largest Rectangle in Histogram 450 65:52
Bfs
Problem Score Companies Time Status
Hotel Service 200 48:48
Stack math
Problem Score Companies Time Status
Evaluate Expression 400
32:46
Rain Water Trapped 400 59:06
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