1381_Design_a_Stack_With_Increment_Operation.cpp

/*
Design a stack which supports the following operations.

Implement the CustomStack class:

CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack or do nothing if the stack reached the maxSize.
void push(int x) Adds x to the top of the stack if the stack hasn't reached the maxSize.
int pop() Pops and returns the top of 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, just 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 customStack = new CustomStack(3); // Stack is Empty []
customStack.push(1);                          // stack becomes [1]
customStack.push(2);                          // stack becomes [1, 2]
customStack.pop();                            // return 2 --> Return top of the stack 2, stack becomes [1]
customStack.push(2);                          // stack becomes [1, 2]
customStack.push(3);                          // stack becomes [1, 2, 3]
customStack.push(4);                          // stack still [1, 2, 3], Don't add another elements as size is 4
customStack.increment(5, 100);                // stack becomes [101, 102, 103]
customStack.increment(2, 100);                // stack becomes [201, 202, 103]
customStack.pop();                            // return 103 --> Return top of the stack 103, stack becomes [201, 202]
customStack.pop();                            // return 202 --> Return top of the stack 102, stack becomes [201]
customStack.pop();                            // return 201 --> Return top of the stack 101, stack becomes []
customStack.pop();                            // return -1 --> Stack is empty return -1.
 

Constraints:

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

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/design-a-stack-with-increment-operation
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
*/

/* O(1) in time and O(N) in space */
#include <stack>
#include <unordered_map>
using namespace std;

class CustomStack {
private:
    stack<int> s;
    unordered_map<int, int> m;
    int _maxSize;
public:
    CustomStack(int maxSize) {
        _maxSize = maxSize;
    }

    void push(int x) {
        if((int)s.size()<_maxSize){
            s.push(x);
        }
    }

    int pop() {
        if(s.empty()) return -1;
        int res = 0;
        unordered_map<int, int>::iterator iter = m.find(s.size());
        if(m.end()!=iter){
            res += iter->second;
            if(iter->first>1){
                m[iter->first-1] += iter->second;
            }
            m.erase(iter);
        }
        res += s.top();
        s.pop();
        return res;
    }

    void increment(int k, int val) {
        k = min(k, (int)s.size());
        if(k>0){
            m[k] += val;
        }
    }
};

/**
 * Your CustomStack object will be instantiated and called as such:
 * CustomStack* obj = new CustomStack(maxSize);
 * obj->push(x);
 * int param_2 = obj->pop();
 * obj->increment(k,val);
 */