Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 25

Description

Min Stack

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(int 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:

• -231 <= val <= 231 - 1
• Methods pop, top and getMin operations will always be called on non-empty stacks.
• At most 3 * 104 calls will be made to push, pop, top, and getMin.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class MinStack {
  vector<int> st;
  vector<int> minSt;
public:
  /** initialize your data structure here. */
  MinStack(){}
  
  void push(int val) {
    st.push_back(val);
    if(minSt.empty() || val <= minSt.back()) {
      minSt.push_back(val);
    }
  }
  
  void pop() {
    if(st.back() == minSt.back()) {
      minSt.pop_back();
    }
    st.pop_back();
  }
  
  int top() {
    return st.back();
  }
  
  int getMin() {
    return minSt.back();
  }
};

// Accepted
// 31/31 cases passed (12 ms)
// Your runtime beats 99.73 % of cpp submissions
// Your memory usage beats 33.29 % of cpp submissions (16.5 MB)