Q30: Min Stack. - DSA Patterns (Multi-Lang)

In Simple Words: Maintain a secondary minStack. Every time a value is pushed, push min(val, minStack.top) onto minStack. getMin() then returns top of minStack in strictly $O(1)$ time.

Time: $O(1)$ for all operations | Space: $O(N)$

Multi-Language SolutionsPython 3 • JavaScript • TypeScript • Java • C++

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class MinStack:
    def __init__(self):
        self.stack = []
        self.min_stack = []

    def push(self, val: int) -> None:
        self.stack.append(val)
        val = min(val, self.min_stack[-1] if self.min_stack else val)
        self.min_stack.append(val)

    def pop(self) -> None:
        self.stack.pop()
        self.min_stack.pop()

    def top(self) -> int:
        return self.stack[-1]

    def getMin(self) -> int:
        return self.min_stack[-1]