LeetCode 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.

使用一个额外的单调栈记录栈中的最小值

class MinStack {
public:
    /** initialize your data structure here. */
    stack<int> stackValue;
    stack<int> stackMin;
    MinStack() {

    }
    
    void push(int x) {
        stackValue.push(x);
        if(stackMin.empty() || x <= stackMin.top())
            stackMin.push(x);
    }
    
    void pop() {
        if(stackMin.top() == stackValue.top())
            stackMin.pop();
        stackValue.pop();
    }
    
    int top() {
        return stackValue.top();
    }
    
    int getMin() {
        return stackMin.top();
    }
};

/**
 * Your MinStack   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();
 */