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.

class MinStack {
public:
    /** initialize your data structure here. */
   
    MinStack() {
        
    }
    
    void push(int x) {
        val.push_back(x);
    }
    
    void pop() {
       val.erase(val.end()-1);
        
    }
    
    int top() {
        int len = val.size();
        return val[len-1];
        
    }
    
    int getMin() {
        int min = val[0];
        if(val.size() == 0)
            return -1;
        else
        {
            
            for(int i = 1; i < val.size(); i++)
            {
                if(val[i] < min)
                {
                    min = val[i];
                }
            }
        }
       return min;
        
    }
private:
     vector<int> val;
};