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写一个循环队列,看看第一个代码错哪里了?为什么会报数组越界?

0
[已解决问题] 解决于 2019-12-27 17:12

package com.test;

public class MyCircularQueue {
int[] data;
int tail;
int head;
int size;

/** Initialize your data structure here. Set the size of the queue to be k. */
public MyCircularQueue(int k) {
    data = new int[k];
    tail = -1;
    head = -1;
    size = 0;

}

/** Insert an element into the circular queue. Return true if the operation is successful. */
public boolean enQueue(int value) {
    if(isFull()){
        return false;
    }
    if(isEmpty()){
        head = 0;
    }
    tail = (tail+1)%data.length;
    data[tail] = value;
    size += 1;
    return true;

}

/** Delete an element from the circular queue. Return true if the operation is successful. */
public boolean deQueue() {
    if(isEmpty()){
        return false;
    }
    if (head == tail) {
        head = -1;
        tail = -1;
        return true;
    }
    head = (head+1)%data.length;
    size -= 1;
    return true;
}

/** Get the front item from the queue. */
public int Front() {
    if(isEmpty()){
        return -1;
    }
    return data[head];

}

/** Get the last item from the queue. */
public int Rear() {//报错位置在这里,报的事数组越界。
    if(isEmpty()){
        return -1;
    }
    return data[tail];
}

/** Checks whether the circular queue is empty or not. */
public boolean isEmpty() {
   // return size == 0?true:false; //用这一句做返回的时候会报数组越界
    return head == -1; //这一句却不会报错
}

/** Checks whether the circular queue is full or not. */
public boolean isFull() {
   // return size == data.length?true:false; //用这一句做返回的时候会报数组越界

    return ((tail + 1) % data.length) == head;//这一句却不会报错
}

}

测试代码如下:

package com.test;

public class test {
public static void main(String[] args) {
MyCircularQueue myCircularQueue = new MyCircularQueue(1);
System.out.println( myCircularQueue.enQueue(1));
System.out.println( myCircularQueue.enQueue(2));
System.out.println( myCircularQueue.enQueue(3));
System.out.println( myCircularQueue.enQueue(4));
System.out.println( myCircularQueue.Rear());
System.out.println( myCircularQueue.isFull());
System.out.println( myCircularQueue.deQueue());
System.out.println( myCircularQueue.enQueue(4));
System.out.println( myCircularQueue.Rear());//这里报错了,报数组越界
}
}

求大神帮忙看看,谢谢

lukely的主页 lukely | 菜鸟二级 | 园豆:218
提问于:2019-07-25 17:18

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小光 7个月前
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最佳答案
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public boolean deQueue() {
        if(isEmpty()){
            return false;
        }
        if (head == tail) {
            head = -1;
            tail = -1;
            return true;
        }
        head = (head+1)%data.length;
        size -= 1;
        return true;
    }

从队列删除元素时if (head == tail) ,只把头和尾两个指针重置了,size -= 1;没有执行

奖励园豆:5
小光 | 小虾三级 |园豆:1830 | 2019-07-26 09:08
其他回答(2)
0

public boolean deQueue() {
if(isEmpty()){
return false;
}
if (head == tail) {
head = -1;
tail = -1;
// 这里没有将size置0,导致使用size做判断的isEmpty/isFull出现逻辑错误
return true;
}
head = (head+1)%data.length;
size -= 1;
return true;
}

静谧的风铃 | 园豆:202 (菜鸟二级) | 2019-07-25 18:05
0

似乎没问题啊

jello chen | 园豆:7091 (大侠五级) | 2019-07-26 06:32
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