Array

                                                                               数组

数组使应用最广泛的数据存储结构。它被植入到大部分编程语言中

    用我的理解来说说数组吧。就行胡萝卜填坑一样，事先准备好坑，然后来一个填一个。拔掉随便一个胡萝卜，则要将拔掉的那个胡萝卜的后面的所有胡萝卜向前移动一位，将拔掉的胡萝卜的坑填住。

    在给胡萝卜排序时，有相同的胡萝卜时的比较次数：

    代码一波：

    查找数组的一个数据项

package Array.Arrays;

public class LowArray {

    private long[] a;

    public LowArray(int size) {

        a = new long[size];
    }

    public void setElem(int index, long value) {
        a[index] = value;
    }

    public long getElem(int index) {
        return a[index];
    }

    public static void main(String[] args) {
        LowArray arr = new LowArray(100);

        int nEilems = 0;
        int j;
        arr.setElem(0, 88);
        arr.setElem(1, 77);
        arr.setElem(2, 99);
        arr.setElem(3, 44);
        arr.setElem(4, 55);
        arr.setElem(5, 22);
        arr.setElem(6, 11);
        arr.setElem(7, 00);
        arr.setElem(8, 86);
        arr.setElem(9, 33);

        nEilems = 10;

        for (j = 0; j < nEilems; j++) {
            System.out.print(arr.getElem(j) + " ");
        }
        System.out.println("");

        int searchKey = 26;
        for (j = 0; j < nEilems; j++)
            if (arr.getElem(j) == searchKey)
                break;

        if (j == nEilems)
            System.out.println("Can't find " + searchKey);
        else
            System.out.println("Found " + searchKey);

        for (j = 0; j < nEilems; j++)
            if (arr.getElem(j) == 26)
                break;


        for (int k = j; k < nEilems; k++)
            arr.setElem(k, arr.getElem(k + 1));
        nEilems--;


        for (j = 0; j < nEilems; j++) {
            System.out.print(arr.getElem(j) + " ");
        }
        System.out.println("");
    }
}

                                    l l      l l

                                    V       V

                                    代码优化

package Array.Arrays;

public class HighArray {

    //数组
    private long a[];
    //数组长度
    private int nElems;

    public HighArray(int max) {
        a = new long[max];
        nElems = 0;
    }

    //查找数据项
    public boolean find(long searchKey) {
        int j;
        for (j = 0; j < nElems; j++)
            if (a[j] == searchKey)
                break;

        if (j == nElems)
            return false;
        else
            return true;
    }


    //添加一个数据
    public void insert(long value) {
        a[nElems] = value;
        nElems++;
    }

    //删除一个数据
    public boolean delete(long value) {
        int j;
        for (j = 0; j < nElems; j++) {
            if (value == a[j])
                break;
        }
        if (j == nElems)
            return false;
        else
            for (int k = j; k < nElems; k++) {
                a[k] = a[k + 1];
            }
        nElems--;
        return true;
    }

    //展示数组
    public void display() {
        for (int j = 0; j < nElems; j++) {
            System.out.print(a[j] + " ");
        }
        System.out.println("");
    }

    public static void main(String[] args) {
        int maxSize = 100;
        HighArray arr = new HighArray(maxSize);
        arr = new HighArray(maxSize);

        arr.insert(77);
        arr.insert(99);
        arr.insert(44);
        arr.insert(55);
        arr.insert(22);
        arr.insert(88);
        arr.insert(11);
        arr.insert(00);
        arr.insert(66);
        arr.insert(33);

        arr.display();

        int searchKey = 35;
        if (arr.find(searchKey)) {
            System.out.println("Fount " + searchKey);
        } else {
            System.out.println("Can't Fount " + searchKey);
        }

        arr.delete(00);
        arr.delete(55);

        arr.display();
    }
}

二分查找：

    首先将数组变为有序数组，然后进行二分查找

package Array.Arrays;

public class OrderArray {

    private long[] a;
    private int nElems;

    public OrderArray(int max) {
        a = new long[max];
        nElems = 0;
    }

    public int size() {
        return nElems;
    }

    public int find(long searchKey) {
        int lowerBound = 0;
        int upperBound = nElems - 1;
        int cirIn;

        while (true) {
            cirIn = (lowerBound + upperBound) / 2;
            if (a[cirIn] == searchKey)
                return cirIn;
            else if (lowerBound > upperBound)
                return nElems;
            else {
                if (a[cirIn] < searchKey)
                    lowerBound = cirIn + 1;
                else
                    upperBound = cirIn - 1;
            }
        }
    }

    public void insert(long value) {
        int j;
        for (j = 0; j < nElems; j++)
            if (a[j] > value)
                break;
        for (int k = nElems; k > j; k--)
            a[k] = a[k - 1];
        a[j] = value;
        nElems++;
    }

    public boolean delete(long value) {
        int j = find(value);
        if (j == nElems)
            return false;
        else
            for (int k = j; k < nElems; k++)
                a[k] = a[k + 1];
        nElems--;
        return true;
    }

    public void display() {
        for (int j = 0; j < nElems; j++)
            System.out.print(a[j] + " ");
        System.out.println("");
    }

    public static void main(String[] args) {
        int maxSize = 100;
        OrderArray arr = new OrderArray(maxSize);

        arr.insert(77);
        arr.insert(99);
        arr.insert(44);
        arr.insert(55);
        arr.insert(22);
        arr.insert(88);
        arr.insert(11);
        arr.insert(00);
        arr.insert(66);
        arr.insert(33);


        arr.display();
        int searKey = 55;

        if (arr.find(searKey) != arr.size())
            System.out.println("Fount " + searKey);
        else
            System.out.println("Can't find " + searKey);


        arr.delete(00);
        arr.display();

    }
}

在插入时则就进行数组的有序化，然后进行二分查找

使用大O表示：

算法	大O表示的运行时间
线性查找	O(N)
二分查找	O(logN)
无序数组的插入	O(1)
有序数组的插入	O(N)
无序数组的删除	O(N)
有序数组的删除	O(N)

关于大O表示的解释：

https://blog.csdn.net/meiLin_Ya/article/details/80906733