Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
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.
模拟实现栈,求取栈中的最小值的方法非常巧妙,可以仔细琢磨琢磨。
class MinStack {
public:
/** initialize your data structure here. */
stack<int> s1,s2;
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();
}
};
/**
* 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();
*/