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:
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.
代码：
class MinStack {
public:
/** initialize your data structure here. */
MinStack() {}
void push(int x) {
s1.push(x);
if (s2.empty() || x <= s2.top()) s2.push(x);
}
void pop() {
if (s1.top() == s2.top()) s2.pop();
s1.pop();
}
int top() {
return s1.top();
}
int getMin() {
return s2.top();
}
private:
stack<int> s1, s2;
};
/**
* 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();
*/
用两个栈来存 $s2$ 用来存最小的 第一次写这样的题 不是很会看了题解才知道怎么写 下次注意！