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.

 

Accepted

277,902

Submissions

771,157

class MinStack {
private:
    stack<int> s1;
    stack<int> s2;
public:
    void push(int x) {
	    s1.push(x);
	    if (s2.empty() || x <= getMin())  s2.push(x);	    
    }
    void pop() {
	    if (s1.top() == getMin())  s2.pop();
	    s1.pop();
    }
    int top() {
	    return s1.top();
    }
    int getMin() {
	    return s2.top();
    }
};
/**
 * 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();
 */

用兩個棧去維護。。一個棧記錄最小的元素。