1 題目理解

要求設(shè)計(jì)一個(gè)雙端循環(huán)隊(duì)列。這個(gè)隊(duì)列能支持以下操作：
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.

2 思路

再次來(lái)做的時(shí)候完全沒(méi)有想法，參考了答案后回過(guò)頭看自己的隊(duì)列文章發(fā)現(xiàn)思路就在文章的循環(huán)隊(duì)列里面講明白了。
重點(diǎn)理解：
1 front表示第一個(gè)數(shù)字有效的位置， tail表示最有一個(gè)有效數(shù)字位置的下一位，也可以理解為要插入一個(gè)元素時(shí)候的位置。這兩個(gè)變量的含義不能變。
2 隊(duì)列為空的條件：front =tail
3 隊(duì)列滿的條件：(tail+1)%capacity=0，是要空出一個(gè)位置的。

class MyCircularDeque {private int capacity ;private int[] values;private int front;private int rear;/** Initialize your data structure here. Set the size of the deque to be k. */public MyCircularDeque(int k) {this.values = new int[k+1];this.capacity = k+1;}/** Adds an item at the front of Deque. Return true if the operation is successful. */public boolean insertFront(int value) {if(isFull()) return false;front = front == 0? capacity-1 :(front-1);values[front] = value;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;values[rear] = value;rear = (rear+1)%capacity;return true;}/** Deletes an item from the front of Deque. Return true if the operation is successful. */public boolean deleteFront() {if(isEmpty()) return false;front = (front+1)%capacity;return true;}/** Deletes an item from the rear of Deque. Return true if the operation is successful. */public boolean deleteLast() {if(isEmpty()) return false;rear = rear==0? capacity-1: rear-1;return true;}/** Get the front item from the deque. */public int getFront() {return !isEmpty()?values[front]:-1;}/** Get the last item from the deque. */public int getRear() {return !isEmpty()?values[rear>0?rear-1:capacity-1]:-1;}/** Checks whether the circular deque is empty or not. */public boolean isEmpty() {return front == rear;}/** Checks whether the circular deque is full or not. */public boolean isFull() {return (rear+1)%capacity==front;} }

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