java常用算法

1

package pack;

public class Demo {
	
	public static void main(String[] args) {
		int[] arr = {321,22,32,4,52,1};
		int temp;
		
		arr = maopao(arr);//冒泡排序
		for (int i : arr) {
			System.out.print(i + ",");
		}
		
		int index = zheban2(arr, 32);
		System.out.println("32的位置是:"+index);
		

	}
	
	//折半查找
	public static int zheban(int[] arr,int key){
		int max,min,mid;
		max=arr.length-1;
		min=0;
		mid=(max+min)/2;
		while(arr[mid]!=key){
			if(key>arr[mid]){
				min=mid+1;	//当key比max还大的时候,算到最后,min=max+1
			}else if(key<arr[mid]){
				max=mid-1;
			}
			
			if(min>max){	//这里要单独判断
				return -1;
			}
			
			mid=(max+min)/2;
		}
		
		return mid;
	}
	//折半查找2
	public static int zheban2(int []arr,int key){
		int min,mid,max;
		max=arr.length-1;
		min=0;
		
		while(min<=max){	//这里注意是<=
			mid = (min+max)/2;
			if(key>arr[mid]){
				min=mid+1;
			}else if(key<arr[mid]){
				max=mid-1;
			}else{
				return mid;
			}
			
		}
		return -1;
	}
	
	//冒泡排序
	public static int[] maopao(int[] arr){
		int temp;
		for(int i=0;i<arr.length-1;i++){
			for(int j=0;j<arr.length-i-1;j++){
				if(arr[j]>arr[j+1]){
					temp = arr[j];
					arr[j] = arr[j+1];
					arr[j+1] = temp;
				}
			}
		}

		return arr;
	}
	
	//选择排序
	public static int[] xuanze(int[] arr){
		int temp;
		for(int i=0;i<arr.length-1;i++){
			for(int j=i+1;j<arr.length;j++){
				if(arr[i]>arr[j]){
					temp = arr[i];
					arr[i] = arr[j];
					arr[j] = temp;
				}
			}
		}

		return arr;
	}
}