Leetcode 1381: Design a Stack With Increment Operation
Design a stack that supports increment operations on its elements. Implement the CustomStack class, which supports adding elements, popping the top element, and incrementing the bottom k elements.
Problem
Approach
Steps
Complexity
Input: The input consists of a series of operations to be performed on the stack, such as push, pop, and increment.
Example: Input: ["CustomStack", "push", "push", "pop", "push", "push", "push", "increment", "increment", "pop", "pop", "pop", "pop"]
Input Data: [[3], [1], [2], [], [2], [3], [4], [5, 100], [2, 100], [], [], [], []]
Constraints:
• The stack can have a maximum of 1000 operations.
• The stack size will be between 1 and 1000 elements.
Output: Return the results of each operation as a list. For 'push', the result is null, for 'pop', the result is the popped element, and for 'increment', the result is null.
Example: [null, null, null, 2, null, null, null, null, null, 103, 202, 201, -1]
Constraints:
• Each output corresponds to the respective input operation.
Goal: The goal is to implement a stack with operations to push elements, pop elements, and increment the bottom k elements by a specified value.
Steps:
• 1. Initialize the stack with a maximum size.
• 2. Implement push operation to add elements to the stack.
• 3. Implement pop operation to remove and return the top element.
• 4. Implement increment operation to increment the bottom k elements by a specified value.
Goal: The solution must efficiently handle a stack with a maximum of 1000 elements and 1000 operations.
Steps:
• All operations must be completed within a reasonable time frame for stacks of size up to 1000.
Assumptions:
• The stack will always have enough capacity to handle the specified operations.
• Input: Input: ["CustomStack", "push", "push", "pop", "push", "push", "push", "increment", "increment", "pop", "pop", "pop", "pop"]
• Explanation: The operations are performed on a stack with a maximum size of 3. The push operations add elements, pop operations remove elements, and the increment operations modify the bottom k elements by adding the specified value.
Approach: The approach is to implement a dynamic stack that supports the basic operations (push, pop) and an increment operation that modifies the bottom k elements.
Observations:
• The stack needs to handle an increment operation that modifies multiple elements efficiently.
• We can use an array to store the stack and perform the increment operation by directly modifying the bottom k elements.
Steps:
• 1. Create a stack array to store the elements.
• 2. Implement the push method to add elements to the stack if it has not exceeded the max size.
• 3. Implement the pop method to return and remove the top element.
• 4. Implement the increment method to add a value to the bottom k elements.
Empty Inputs:
• If no operations are performed, the stack remains empty.
Large Inputs:
• Ensure the solution works for the maximum allowed size of the stack and number of operations.
Special Values:
• The increment value should be between 0 and 100, and the number of elements to increment should be within the size of the stack.
Constraints:
• The stack should never exceed the maximum size, and operations should be efficient.
int ptr, m;
public:
CustomStack(int mx) {
stk.resize(mx);
ptr = -1;
m = mx;
}
void push(int x) {
if (ptr < m - 1) {
ptr++;
stk[ptr] = x;
}
}
int pop() {
if(ptr == -1) return -1;
return stk[ptr--];
}
void increment(int k, int val) {
for(int i = 0; i < min(m, k); i++)
stk[i] += 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);
1 : Variable Initialization
int ptr, m;
Initialize the pointer `ptr` for stack manipulation and the maximum size `m` of the stack.
2 : Access Control
public:
Public access to the methods and constructor of the class.
3 : Constructor
CustomStack(int mx) {
Constructor to initialize the stack with a maximum size.
4 : Stack Initialization
stk.resize(mx);
Resize the stack `stk` to the given size `mx`.
5 : Variable Initialization
ptr = -1;
Initialize the pointer `ptr` to -1 to indicate the stack is empty.
6 : Variable Initialization
m = mx;
Set the maximum size of the stack to the provided value `mx`.
7 : Method Definition
void push(int x) {
Define the `push` method to add an element to the stack.
8 : Conditional Check
if (ptr < m - 1) {
Check if the stack is not full.
9 : Pointer Manipulation
ptr++;
Increment the pointer `ptr` to add an element to the stack.
10 : Stack Operation
stk[ptr] = x;
Assign the value `x` to the stack at position `ptr`.
11 : Method Definition
int pop() {
Define the `pop` method to remove an element from the stack.
12 : Conditional Check
if(ptr == -1) return -1;
Check if the stack is empty and return -1 if true.
13 : Pointer Manipulation
return stk[ptr--];
Return the top element of the stack and decrement the pointer `ptr`.
14 : Method Definition
void increment(int k, int val) {
Define the `increment` method to increment the first `k` elements by the value `val`.
15 : Looping
for(int i = 0; i < min(m, k); i++)
Loop through the first `k` elements, but no more than the stack size `m`.
16 : Stack Manipulation
stk[i] += val;
Increment each element in the stack by the value `val`.
Best Case: O(1) for push and pop operations.
Average Case: O(k) for the increment operation, where k is the number of elements to increment.
Worst Case: O(k) for the increment operation.
Description: The increment operation has a time complexity of O(k) because we need to modify the bottom k elements.
Best Case: O(n) in all cases since we store the stack elements.
Worst Case: O(n) where n is the maximum size of the stack.
Description: The space complexity is O(n), where n is the number of elements in the stack.
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