Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
Implement the `MinStack` class:
- `MinStack()` initializes the stack object.
- `void push(int val)` pushes the element `val` onto the stack.
- `void pop()` removes the element on the top of the stack.
- `int top()` gets the top element of the stack.
- `int getMin()` retrieves the minimum element in the stack.
You must implement a solution with `O(1)` time complexity for each function.
Examples
Example 1
Input:
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]Output:
[null,null,null,null,-3,null,0,-2]MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); // return -3
minStack.pop();
minStack.top(); // return 0
minStack.getMin(); // return -2
Constraints
- •
-2^31 <= val <= 2^31 - 1 - •
Methods pop, top and getMin operations will always be called on non-empty stacks. - •
At most 3 * 10^4 calls will be made to push, pop, top, and getMin.
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