[LeetCode] 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.

分析：用两个栈来实现

class MinStack {
// normal stack
Stack<Integer> st = new Stack<Integer>();
// min value stack
Stack<Integer> stm = new Stack<Integer>();

public void push(int x) {
st.push(x);
if (stm.isEmpty() || stm.peek() >= x)
stm.push(x);
}

public void pop() {
int peek = st.peek();
st.pop();
if (peek <= stm.peek())
stm.pop();
}

public int top() {
return st.peek();
}

public int getMin() {
return stm.peek();
}
}