JAVA顺序查找、二分查找

最新推荐文章于 2022-11-28 14:57:36 发布

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本文详细介绍了两种基本的查找算法：顺序查找与二分查找。顺序查找适用于未排序的数组，其时间复杂度为O(n)，空间复杂度为O(1)；而二分查找则针对已排序的数组，采用迭代与递归两种方式实现，时间复杂度为O(logn)，空间复杂度分别为O(1)与O(logn)。通过具体的代码实例，读者可以深入理解这两种查找算法的工作原理。

/*
 * 顺序查找
 * T(n)=O(n)
 * S(n)=O(1)
 */
public class TestSearch01 {
	public static void main(String[] args){
		int[] scoreArr = {89,45,78,78,45,100,98,86,100,65};
		int score = 100;
		int index = search(scoreArr,score);
		if(index==-1){
			System.out.print("该分数不存在");
		}else{
			System.out.print(score+"的索引是"+index);
		}	
		
	}
	public static int search(int[] scoreArr,int score){
		for(int i=0;i<scoreArr.length;i++){
			if(scoreArr[i]==score){
				return i;
			}
		}
		return -1;		
	}
}

二分查找

public class TestBinarySearch {
	public static void main(String[] args){
		int[] array = {1,2,3,4,5,6,7,8,9,10};
		int key = 6;		
		int index1 = binary1(array,key);
		if(index1==-1){
			System.out.print("该分数不存在");
		}else{
			System.out.println(key+"的索引是"+index1);
		}				
	}
		
	/*
	 * 不使用递归的二分查找
	 * T(n)=O(logn)
	 * S(n)=O(1)	
	 * 
	 */
	
	public static int binary1(int[] array,int key){
			int low = 0;
			int high = array.length-1;
			
			while(low<=high){
				int mid = (low+high)/2;
				if(key==array[mid]){
					return mid;
				}else if(key<array[mid]){
					high=mid-1;
				}else{
					low=mid+1;
				}
			}
			return -1;
		} 
	
	
	/*
	 * 使用递归查找
	 * T(n)=O(logn)
	 * S(n)=O(logn)
	 *  
	 */
	
	public static int dbinary2(int[] array,int key){
		int low = 0;
		int high = array.length-1;
		return dbinary2(array,key,low,high);
	}
	
	public static int dbinary2(int[] array,int key,int low ,int high){
		if(low>high){
			return -1;			
		}
		int mid = (low+high)/2;
		if(key==array[mid]){
			return mid;			
		}else if(key<array[mid]){
			return dbinary(array, key, low, mid-1);
		}else{
			return dbinary(array, key, mid+1, high);
		}
	}
}