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

September LeetCoding Challenge 30

Description

Design a Stack With Increment Operation

Design a stack that supports increment operations on its elements.

Implement the CustomStack class:

• CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack.
• void push(int x) Adds x to the top of the stack if the stack has not reached the maxSize.
• int pop() Pops and returns the top of the stack or -1 if the stack is empty.
• void inc(int k, int val) Increments the bottom k elements of the stack by val. If there are less than k elements in the stack, increment all the elements in the stack.

Example 1:

Input
["CustomStack","push","push","pop","push","push","push","increment","increment","pop","pop","pop","pop"]
[[3],[1],[2],[],[2],[3],[4],[5,100],[2,100],[],[],[],[]]
Output
[null,null,null,2,null,null,null,null,null,103,202,201,-1]
Explanation
CustomStack stk = new CustomStack(3); // Stack is Empty []
stk.push(1);                          // stack becomes [1]
stk.push(2);                          // stack becomes [1, 2]
stk.pop();                            // return 2 --> Return top of the stack 2, stack becomes [1]
stk.push(2);                          // stack becomes [1, 2]
stk.push(3);                          // stack becomes [1, 2, 3]
stk.push(4);                          // stack still [1, 2, 3], Do not add another elements as size is 4
stk.increment(5, 100);                // stack becomes [101, 102, 103]
stk.increment(2, 100);                // stack becomes [201, 202, 103]
stk.pop();                            // return 103 --> Return top of the stack 103, stack becomes [201, 202]
stk.pop();                            // return 202 --> Return top of the stack 202, stack becomes [201]
stk.pop();                            // return 201 --> Return top of the stack 201, stack becomes []
stk.pop();                            // return -1 --> Stack is empty return -1.

Constraints:

• 1 <= maxSize, x, k <= 1000
• 0 <= val <= 100
• At most 1000 calls will be made to each method of increment, push and pop each separately.

Solution

class CustomStack {
  vector<int> incremental;
  vector<int> container;
  int cap;
public:
  CustomStack(int maxSize): cap(maxSize) {}
  
  void push(int x) {
    if(container.size() == cap) return;
    container.push_back(x);
    incremental.push_back(0);
  }
  
  int pop() {
    if(container.empty()) return -1;
    int result = container.back() + incremental.back();
    container.pop_back();
    if(incremental.size() > 1) incremental[incremental.size() - 2] += incremental.back();
    incremental.pop_back();
    return result;
  }
  
  void increment(int k, int val) {
    if(container.empty()) return;
    k = min<int>(k - 1, container.size() - 1);
    incremental[k] += val;
  }
};