2020/07/14-Array-interpolation, deletion, insertion sort, selection sort
1. Add a number to a sequence of sorted arrays, and still maintain the original sorting method
Ideas:
- (If the starting array is 3 digits and 1 digit needs to be added, then rebuild a 4-digit array,
- The reason for rebuilding a larger array is that when you first created the array, you didn’t know how many digits to add later.
- Therefore, only the required number of array lengths are created at the beginning)
- Idea: Adding elements to the element group needs to increase or decrease the array capacity
- If you increase the number by 1, you need to redefine an array that is 1 bit larger than before
- Then use the for loop to assemble the previous number into the new array
- The last bit of the new array is empty
public class demo4 {
public static void main(String[] args) {
int[] a = {
99,85,45,56,21};
int[] b = new int[6];
for (int i = 0; i < a.length; i++) {
b[i] = a[i];//b的最后一位没有赋值，相当于空，默认是0，
// 之后往里面添加数字相当于覆盖
}
System.out.println(Arrays.toString(b));
Scanner sc = new Scanner(System.in);
System.out.println("请输入一个数：");
int num = sc.nextInt();
boolean isInsert = false;
for (int i = b.length-2; i >=0; i--) {
//-2是因为b本身大一位，且下标需小一位
if(num>b[i]){
//从后向前遍历，从大到小排序，将更小的数放进数组b的最后一个空位
b[i+1]=b[i];//下标后移
}else {
b[i+1]=num;
isInsert = true;
break;
}
}
if(isInsert==false){
//原数组所有数都比新增加的数小，故将新增加的数放在首位
b[0]=num;
}
System.out.println(Arrays.toString(b));
}
}
Two, delete a number from the array
Ideas:
- Similar to adding a number to the array, re-create a new array with a smaller one
- Type the subscript of the number you want to delete in the array
- Use the for loop to put the numbers in the original array into the new array until i= the subscript,
- contiune skips this cycle.
public class test3 {
public static void main(String[] args) {
int[] a = {
99,85,80,63,60};
int[] b = new int[4];
Scanner sc = new Scanner(System.in);
System.out.println("请输入要删除的下标：");
int num = sc.nextInt();
int j = 0;
for (int i = 0; i < a.length; i++) {
if(i==num) continue;
b[i] = a[i];
j++;
}
System.out.println(Arrays.toString(b));
}
}
3. Sort a string of given array elements in ascending order using the selection sort method
- [Basic sorting methods: select sorting, bubble sorting, insertion sorting] [Advanced sorting algorithms: quick sorting, merge sorting]
- Ideas:
- The outer loop defines the minimum value of each a[i] value, compares the a[i] value with each subsequent value, and marks the minimum value and the minimum value subscript
- Assign a[i] defined by the outer loop to the array corresponding to the subscript of the marked minimum value, and then assign the marked minimum value to a[i]
- This requires the introduction of a variable to store the subscript
- It should be noted that when defining the variable, it cannot be defined as 1, or a fixed value.
- Instead, it should be defined as i, because it does not necessarily produce exchanges every time comparison, and it may keep the original position unchanged.
public class demo5 {
public static void main(String[] args) {
/*
选择排序逻辑：
从前向后对每一个下表对应的元素作为基准值
与后面所有的元素进行比较，找出最小值
与当前下标的元素进行交换
进行下一次循环
*/ int[] a={
7,6,2,5,8,4,12,3};
//i代表选取的基准位，j代表的在动的
for(int i=0;i<a.length-1;i++){
int min=a[i];
int tmp=i;
for (int j = i; j <a.length ; j++) {
if(min>a[j]){
min=a[j];
tmp=j;
}
}
a[tmp]=a[i];
a[i]=min;
}
System.out.println(Arrays.toString(a));
}
}
Four, insertion sort method
- Idea: The outer loop starts from item 2, and compares it with the previous number each time.
- For example: a[1]: compare a[0], if a[1] is big, assign a[0] to a[1]
- a[2]: Compare with 0, 1 subscript array
public class demo6 {
public static void main(String[] args) {
/*
逻辑：从第二位开始，向前比较，进行插入逻辑
*/
boolean isInsert = false;
int[] a = {
1,3,8,2,5,7};
for (int i = 1; i < a.length; i++) {
int tmp = a[i];
for (int j = i-1; j >=0 ; j--) {
//如果遇到比自己大的，大的值就后移
// 如果遇到比自己小的，就在后方插入
//如果一直没有插入，就插入首位
if(tmp<a[j]){
a[j+1]=a[j];
}else
{
a[j+1]=tmp;
isInsert = true;
break;}
}
if (isInsert!=true){
a[0]=tmp;
}
}
System.out.println(Arrays.toString(a));
}
}