155. 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:
MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); --> Returns -3. minStack.pop(); minStack.top(); --> Returns 0. minStack.getMin(); --> Returns -2.
这道题没c#的,所以用Java写的。用两个stack,一个存push的值,另外一个用来存最小值。Pop的时候,如果正常stack pop的值小于等于另一个存最小值的stack,最小值的stack也pop
public class MinStack { private Stack _stack; private Stack _stackMin; /** initialize your data structure here. */ public MinStack() { _stack = new Stack(); _stackMin = new Stack(); } public void push(int x) { _stack.push(x); if(_stackMin.isEmpty() || (int)_stackMin.peek() >= x) { _stackMin.push(x); } } public void pop() { if(!_stack.isEmpty() && (int)_stack.pop() <= (int)_stackMin.peek()) _stackMin.pop(); } public int top() { if(_stack.isEmpty()) return 0; return (int)_stack.peek(); } public int getMin() { if(_stackMin.isEmpty()) return 0; return (int)_stackMin.peek(); } }