数组常见操作

数组的定义

int[] arr = new int[5];
int[] arr = new int[]{1,2,3,4}
int[] arr = {1,2,3,4}

取数组中的最值

    public static void main(String[] args) {

        int[] va = {45,7,67,87,98,0,45,78,100};

        int tmp = va[0];

        for(int i=1;i<va.length;i++){
            if(tmp<va[i]){
                 tmp = va[i];
                 i++;
            }
        }

       System.out.println(tmp);  //最大值
    }

选择排序

 public static void main(String[] args) {

        int[] va = {45,7,67,87,98,0,45,78,100};

        int tmp=va[0];

        for(int i=0;i<va.length-1;i++){
            for(int y=i+1;y<va.length;y++){
                if(va[i]>va[y]){
                    tmp = va[i];
                    va[i] = va[y];
                    va[y] = tmp;
                }
            }
        }

        for(int i:va){
            System.out.print(i);
            System.out.print("  ");
        }

    }

冒泡排序

        public static void main(String[] args) {

        int[] va = {45,7,67,87,98,0,45,78,100};


        int tmp=va[0];

        for(int i=0;i<va.length-1;i++){
            for(int y=0;y<va.length-1-i;y++){
                if(va[y] > va[y+1]){
                    tmp = va[y];
                    va[y] = va[y+1];
                    va[y+1] = tmp;
                }
            }
        }

        for(int i:va){
            System.out.print(i);
            System.out.print("  ");
        }
    }

二分法查找

 public static void main(String[] args) {

      int[] arr = {1,2,56,78,98,101,120};

        System.out.println(halfSearch(arr,120));

    }


    public static int  halfSearch(int[] arr,int key){

        int min,mid,max;
        min = 0;
        max= arr.length-1;
        mid = (min+max)/2;

        while(arr[mid]!=key){
             if(arr[mid]>key){
                 max = mid-1;
             }else if(arr[mid]<key){
                 min = mid+1;
             }

            if(max<min){
                return  -1;
            }

            mid = (min+max)/2;
        }

        return  mid;

    }