![https://leetcode.com/problems/min-stack/]
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
- push(x) – Push element x onto stack.
- pop() – Removes the element on top of the stack.
- top() – Get the top element.
- getMin() – Retrieve the minimum element in the stack.
Example 1:
Input
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]
Output
[null,null,null,null,-3,null,0,-2]
Explanation
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:
- Methods pop, top and getMin operations will always be called on non-empty stacks.
class MinStack {
private List<Integer> stack = new ArrayList<>();
private List<Integer> min = new ArrayList<>();
/** initialize your data structure here. */
public MinStack() {
}
public void push(int x) {
stack.add(x);
int prev = min.size() > 0 ? min.get(min.size() - 1): Integer.MAX_VALUE;
min.add(Math.min(prev, x));
}
public void pop() {
stack.remove(stack.size() - 1);
min.remove(min.size() - 1);
}
public int top() {
return stack.get(stack.size() - 1);
}
public int getMin() {
return min.get(min.size() - 1);
}
}
/**
* Your MinStack object will be instantiated and called as such:
* MinStack obj = new MinStack();
* obj.push(x);
* obj.pop();
* int param_3 = obj.top();
* int param_4 = obj.getMin();
*/