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1381. Design a Stack With Increment Operation

Description

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.

Solutions

Solution 1: Array Simulation

We can use an array $stk$ to simulate the stack, and an integer $i$ to represent the position of the next element to be pushed into the stack. In addition, we need another array $add$ to record the cumulative increment value at each position.

When calling $push(x)$, if $i < maxSize$, we put $x$ into $stk[i]$ and increment $i$ by one.

When calling $pop()$, if $i \leq 0$, it means the stack is empty, so we return $-1$. Otherwise, we decrement $i$ by one, and the answer is $stk[i] + add[i]$. Then we add $add[i]$ to $add[i - 1]$, and set $add[i]$ to zero. Finally, we return the answer.

When calling $increment(k, val)$, if $i > 0$, we add $val$ to $add[\min(i, k) - 1]$.

The time complexity is $O(1)$, and the space complexity is $O(n)$. Where $n$ is the maximum capacity of the stack.

  • class CustomStack {
        private int[] stk;
        private int[] add;
        private int i;
    
        public CustomStack(int maxSize) {
            stk = new int[maxSize];
            add = new int[maxSize];
        }
    
        public void push(int x) {
            if (i < stk.length) {
                stk[i++] = x;
            }
        }
    
        public int pop() {
            if (i <= 0) {
                return -1;
            }
            int ans = stk[--i] + add[i];
            if (i > 0) {
                add[i - 1] += add[i];
            }
            add[i] = 0;
            return ans;
        }
    
        public void increment(int k, int val) {
            if (i > 0) {
                add[Math.min(i, k) - 1] += 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);
     */
    
  • class CustomStack {
    public:
        CustomStack(int maxSize) {
            stk.resize(maxSize);
            add.resize(maxSize);
            i = 0;
        }
    
        void push(int x) {
            if (i < stk.size()) {
                stk[i++] = x;
            }
        }
    
        int pop() {
            if (i <= 0) {
                return -1;
            }
            int ans = stk[--i] + add[i];
            if (i > 0) {
                add[i - 1] += add[i];
            }
            add[i] = 0;
            return ans;
        }
    
        void increment(int k, int val) {
            if (i > 0) {
                add[min(k, i) - 1] += val;
            }
        }
    
    private:
        vector<int> stk;
        vector<int> add;
        int i;
    };
    
    /**
     * 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);
     */
    
  • class CustomStack:
    
        def __init__(self, maxSize: int):
            self.stack = []
            self.max_size = maxSize
            self.inc = []
    
        def push(self, x: int) -> None:
            if len(self.stack) < self.max_size:
                self.stack.append(x)
                self.inc.append(0)
                # 0 because no range operation
                # not append(inc[-1]), since it will be updated on pop()
    
        def pop(self) -> int:
            if not self.stack: return -1
            if len(self.inc) > 1:
                self.inc[-2] += self.inc[-1]
            return self.inc.pop() + self.stack.pop()
    
        def increment(self, k: int, val: int) -> None:
            if self.inc:
                self.inc[min(k, len(self.inc)) -1] += val
    
    # Your CustomStack object will be instantiated and called as such:
    # obj = CustomStack(maxSize)
    # obj.push(x)
    # param_2 = obj.pop()
    # obj.increment(k,val)
    
    ###############
    
    class CustomStack:
        def __init__(self, maxSize: int):
            self.stk = [0] * maxSize
            self.add = [0] * maxSize
            self.i = 0
    
        def push(self, x: int) -> None:
            if self.i < len(self.stk):
                self.stk[self.i] = x
                self.i += 1
    
        def pop(self) -> int:
            if self.i <= 0:
                return -1
            self.i -= 1
            ans = self.stk[self.i] + self.add[self.i]
            if self.i > 0:
                self.add[self.i - 1] += self.add[self.i]
            self.add[self.i] = 0
            return ans
    
        def increment(self, k: int, val: int) -> None:
            i = min(k, self.i) - 1
            if i >= 0:
                self.add[i] += val
    
    
    # Your CustomStack object will be instantiated and called as such:
    # obj = CustomStack(maxSize)
    # obj.push(x)
    # param_2 = obj.pop()
    # obj.increment(k,val)
    
    
  • type CustomStack struct {
    	stk []int
    	add []int
    	i   int
    }
    
    func Constructor(maxSize int) CustomStack {
    	return CustomStack{make([]int, maxSize), make([]int, maxSize), 0}
    }
    
    func (this *CustomStack) Push(x int) {
    	if this.i < len(this.stk) {
    		this.stk[this.i] = x
    		this.i++
    	}
    }
    
    func (this *CustomStack) Pop() int {
    	if this.i <= 0 {
    		return -1
    	}
    	this.i--
    	ans := this.stk[this.i] + this.add[this.i]
    	if this.i > 0 {
    		this.add[this.i-1] += this.add[this.i]
    	}
    	this.add[this.i] = 0
    	return ans
    }
    
    func (this *CustomStack) Increment(k int, val int) {
    	if this.i > 0 {
    		this.add[min(k, this.i)-1] += val
    	}
    }
    
    /**
     * Your CustomStack object will be instantiated and called as such:
     * obj := Constructor(maxSize);
     * obj.Push(x);
     * param_2 := obj.Pop();
     * obj.Increment(k,val);
     */
    
  • class CustomStack {
        private stk: number[];
        private add: number[];
        private i: number;
    
        constructor(maxSize: number) {
            this.stk = Array(maxSize).fill(0);
            this.add = Array(maxSize).fill(0);
            this.i = 0;
        }
    
        push(x: number): void {
            if (this.i < this.stk.length) {
                this.stk[this.i++] = x;
            }
        }
    
        pop(): number {
            if (this.i <= 0) {
                return -1;
            }
            const ans = this.stk[--this.i] + this.add[this.i];
            if (this.i > 0) {
                this.add[this.i - 1] += this.add[this.i];
            }
            this.add[this.i] = 0;
            return ans;
        }
    
        increment(k: number, val: number): void {
            if (this.i > 0) {
                this.add[Math.min(this.i, k) - 1] += val;
            }
        }
    }
    
    /**
     * Your CustomStack object will be instantiated and called as such:
     * var obj = new CustomStack(maxSize)
     * obj.push(x)
     * var param_2 = obj.pop()
     * obj.increment(k,val)
     */
    
    

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