155.MinStack.cpp

/*
 * @lc app=leetcode id=155 lang=cpp
 *
 * [155] Min Stack
 *
 * https://leetcode.com/problems/min-stack/description/
 *
 * algorithms
 * Easy (46.31%)
 * Likes:    4897
 * Dislikes: 462
 * Total Accepted:    708.6K
 * Total Submissions: 1.5M
 * Testcase Example:
 * '["MinStack","push","push","push","getMin","pop","top","getMin"]\n[[],[-2],[0],[-3],[],[],[],[]]'
 *
 * Design a stack that supports push, pop, top, and retrieving the minimum
 * element in constant time.
 *
 * Implement the MinStack class:
 *
 *
 * MinStack() initializes the stack object.
 * void push(val) pushes the element val onto the stack.
 * void pop() removes the element on the top of the stack.
 * int top() gets the top element of the stack.
 * int getMin() retrieves the minimum element in the stack.
 *
 *
 *
 * Example 1:
 *
 *
 * Input
 * ["MinStack","push","push","push","getMin","pop","top","getMin"]
 * [[],[-2],[0],[-3],[],[],[],[]]
 *
 * Output
 * [null,null,null,null,-3,null,0,-2]
 *
 * Explanation
 * MinStack minStack = new MinStack();
 * minStack.push(-2);
 * minStack.push(0);
 * minStack.push(-3);
 * minStack.getMin(); // return -3
 * minStack.pop();
 * minStack.top();    // return 0
 * minStack.getMin(); // return -2
 *
 *
 *
 * Constraints:
 *
 *
 * -2^31 <= val <= 2^31 - 1
 * Methods pop, top and getMin operations will always be called on non-empty
 * stacks.
 * At most 3 * 10^4 calls will be made to push, pop, top, and getMin.
 *
 *
 */

// @lc code=start
#include <vector>

class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {}

    void push(int val) {
        all_.push_back(val);
        if (min_.empty() || min_.back() >= val) {
            min_.push_back(val);
        }
    }

    void pop() {
        int val = all_.back();
        if (val == min_.back()) min_.pop_back();
        all_.pop_back();
    }

    int top() { return all_.back(); }

    int getMin() { return min_.back(); }

private:
    std::vector<int> min_;
    std::vector<int> all_;
};

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack* obj = new MinStack();
 * obj->push(val);
 * obj->pop();
 * int param_3 = obj->top();
 * int param_4 = obj->getMin();
 */
// @lc code=end