LeetCode 641. Design Circular Deque
2024-09-07 20:30:54
原题链接在这里：https://leetcode.com/problems/design-circular-deque/
题目：
Design your implementation of the circular double-ended queue (deque).
Your implementation should support following operations:
MyCircularDeque(k): Constructor, set the size of the deque to be k.insertFront(): Adds an item at the front of Deque. Return true if the operation is successful.insertLast(): Adds an item at the rear of Deque. Return true if the operation is successful.deleteFront(): Deletes an item from the front of Deque. Return true if the operation is successful.deleteLast(): Deletes an item from the rear of Deque. Return true if the operation is successful.getFront(): Gets the front item from the Deque. If the deque is empty, return -1.getRear(): Gets the last item from Deque. If the deque is empty, return -1.isEmpty(): Checks whether Deque is empty or not.isFull(): Checks whether Deque is full or not.
Example:
MyCircularDeque circularDeque = new MycircularDeque(3); // set the size to be 3
circularDeque.insertLast(1); // return true
circularDeque.insertLast(2); // return true
circularDeque.insertFront(3); // return true
circularDeque.insertFront(4); // return false, the queue is full
circularDeque.getRear(); // return 2
circularDeque.isFull(); // return true
circularDeque.deleteLast(); // return true
circularDeque.insertFront(4); // return true
circularDeque.getFront(); // return 4
Note:
- All values will be in the range of [0, 1000].
- The number of operations will be in the range of [1, 1000].
- Please do not use the built-in Deque library.
题解：
Use an array to maintain values.
start index pointing to queue head, initialized as -1.
end index pointing to queue tail, initialized as -1.
When insertFront, if start == -1, assign start as 0, else start = (start - 1 + k) % k. Assign new value to arr[start]. If end is -1, need to update end = start. This only happens at the beginning.
When insertLast, end = (end + 1) % k. Assign new value to arr[end]. If start is -1, need to update start = end. This only happends at the begining.
deleteFront, move start + 1.
deleteLast, move end - 1.
Time Complexity: MyCircularDeque, O(1). insertFront, O(1). insertLast, O(1). deleteFront, O(1). deleteLast, O(1). getFront, O(1). getRear, O(1). isEmpty, O(1). isEmpty, O(1).
Space: O(k).
AC Java:
class MyCircularDeque {
int [] arr;
int start;
int end;
int len;
int k;
/** Initialize your data structure here. Set the size of the deque to be k. */
public MyCircularDeque(int k) {
arr = new int[k];
start = -1;
end = -1;
len = 0;
this.k = k;
}
/** Adds an item at the front of Deque. Return true if the operation is successful. */
public boolean insertFront(int value) {
if(isFull()){
return false;
}
if(start == -1){
start = 0;
}else{
start = (start - 1 + k) % k;
}
arr[start] = value;
if(end == -1){
end = start;
}
len++;
return true;
}
/** Adds an item at the rear of Deque. Return true if the operation is successful. */
public boolean insertLast(int value) {
if(isFull()){
return false;
}
end = (end + 1) % k;
arr[end] = value;
if(start == -1){
start = end;
}
len++;
return true;
}
/** Deletes an item from the front of Deque. Return true if the operation is successful. */
public boolean deleteFront() {
if(isEmpty()){
return false;
}
start = (start + 1) % k;
len--;
return true;
}
/** Deletes an item from the rear of Deque. Return true if the operation is successful. */
public boolean deleteLast() {
if(isEmpty()){
return false;
}
end = (end - 1 + k) % k;
len--;
return true;
}
/** Get the front item from the deque. */
public int getFront() {
return isEmpty() ? -1 : arr[start];
}
/** Get the last item from the deque. */
public int getRear() {
return isEmpty() ? -1 : arr[end];
}
/** Checks whether the circular deque is empty or not. */
public boolean isEmpty() {
return len == 0;
}
/** Checks whether the circular deque is full or not. */
public boolean isFull() {
return len == k;
}
}
/**
* Your MyCircularDeque object will be instantiated and called as such:
* MyCircularDeque obj = new MyCircularDeque(k);
* boolean param_1 = obj.insertFront(value);
* boolean param_2 = obj.insertLast(value);
* boolean param_3 = obj.deleteFront();
* boolean param_4 = obj.deleteLast();
* int param_5 = obj.getFront();
* int param_6 = obj.getRear();
* boolean param_7 = obj.isEmpty();
* boolean param_8 = obj.isFull();
*/
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