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.
思路:用栈
class MinStack {
public:
void push(int x) {
if(mins.empty() || x <= mins.top())
mins.push(x);
s.push(x);
} void pop() {
if(!s.empty() && !mins.empty() && s.top() == mins.top())
mins.pop();
s.pop();
} int top() {
return s.top();
} int getMin() {
return mins.top();
}
private:
stack<int> s;
stack<int> mins;
};