第一周 周六

无甚可讲,上练习.

对一个给定的数组实现冒泡排序

import java.util.Arrays;
public class Bubble {
    public static int[] bubble(int arr[]){
        for(int i=0;i< arr.length-1;i++){
            boolean a = false;
            for(int j=0; j< (arr.length-1-i);j++){
                if(arr[j]>arr[j+1]){
                    int t=0;
                    t=arr[j+1];
                    arr[j+1]=arr[j];
                    arr[j]=t;
                    a = true;
                }
            }
            if (a==false){
                break;
            }
        }
        return arr;
    }
    public static void main(String[] args){
        int arr[]={12,5,48,26,19,6};
        int[] ret = arr;
        System.out.println(Arrays.toString(arr));
        bubble(ret);
        System.out.println(Arrays.toString(ret));
    }
}

对一个给定的有序数组进行二分查找

public class BinarySearch {
    public static int binarySearch(int[] arr,int key) {
        int i=0; int j=arr.length-1;
        while(i<=j){
            int mid =(i+j)/2;
            if(arr[mid]key){
                j=mid-1;
            }else{
                return mid;
            }
        }
        return -1;
    }
    public static void main(String[] args) {
        int[] arr = {1,2,3,4,5};
        System.out.println("所寻数字在a["+binarySearch(arr,4)+"]处");
    }
}

若一数组内两元素相加为N,求着这两元素的坐标.

public class Sum {
    public static int[]sum (int[] arr, int key) {
        int a = 0;int b=0;int c=0;
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr.length; j++) {
                if(i==j){
                    continue;
                }
                if ( arr[i] + arr[j]==key) {
                    a = i ; b = j;
                    break;
                }
            }

        }
        int[] ret={b,a};
        return ret;
    }

    public static void main(String[] args) {
        int arr[] = {4, 7, 11, 15};
        System.out.print(Arrays.toString(arr));
        System.out.println(" 中相加等于22的两个数组坐标是:");
        System.out.println(" " + Arrays.toString(sum(arr, 22)));
    }
}