Imagine a (literal) stack of plates. If the stack gets too high, it might topple. Therefore, in real life, we would likely start a new stack when the previous stack exceeds some threshold. Implement a data structure SetOfStacks that mimics this. SetOfStacks should be composed of several stacks and should create a new stack once the previous one exceeds capacity. SetOfStacks.push() and SetOfStacks.pop() should behave identically to a single stack (that is, pop() should return the same values as it would if there were just a single stack). Follow Up: Implement a function popAt(int index) which performs a pop operation on a specific sub-stack.
You should delete the sub-stack when it becomes empty. pop, popAt should return -1 when there's no element to pop.
Example1:
Input: ["StackOfPlates", "push", "push", "popAt", "pop", "pop"] [[1], [1], [2], [1], [], []] Output: [null, null, null, 2, 1, -1] Explanation:
Example2:
Input: ["StackOfPlates", "push", "push", "push", "popAt", "popAt", "popAt"] [[2], [1], [2], [3], [0], [0], [0]] Output: [null, null, null, null, 2, 1, 3]