java实现二分查找

java实现二分查找

任意数组，先用快速排序进行排序，再二分查找给定数字

public class Test02 {
	//记录查找的次数
	static int count = 0;
	public static void main(String[] args) {
		int[] nums={51,20,32,45,85,16,47};
		System.out.println("原数组：");
		print(nums);
		//快速排序
		quickSort(nums,0,nums.length-1);
		System.out.println("排序后数组：");
		print(nums);
		//折半查找（二分查找）
		int fNum = 2;
		count++;
		int n = binaryFind(nums,0,nums.length-1,fNum);
		if(n==-1){
			System.out.println("次数组不存在数字："+fNum);
		}else{
			System.out.println("要查找的数字为："+fNum);
			System.out.println("查找次数为："+count);
			System.out.println("下标为："+n);
		}
	}

	private static int binaryFind(int[] nums, int start, int end, int key) {
		int middleNum = (end - start)/2 + start;
		if(key == nums[middleNum]){
			return middleNum;
		}
		if(start>end){
			return -1;
		}else if(key>nums[middleNum]){
			count++;
			return binaryFind(nums, middleNum+1, end, key);
		}else{
			count++;
			return binaryFind(nums, start, middleNum-1, key);
		}
	}

	private static void quickSort(int[] nums, int start, int end) {
		int sStart = start;
		int eEnd = end;
		int key = nums[start];
		while(eEnd>sStart){
			while(eEnd>sStart && nums[eEnd]>=key){
				eEnd--;
			}
			if(nums[eEnd]<=key){
				int temp = nums[eEnd];
				nums[eEnd] = nums[sStart];
				nums[sStart] = temp;
			}
			while(eEnd > sStart && nums[sStart]<=key){
				sStart++;
			}
			if(nums[sStart]>=key){
				int temp = nums[sStart];
				nums[sStart] = nums[eEnd];
				nums[eEnd] = temp;
			}
		}
		if(sStart>start){
			quickSort(nums, start, sStart-1);
		}
		if(eEnd<end){
			quickSort(nums, eEnd+1, end);
		}
	}

	private static void print(int[] nums) {
		for (int i : nums) {
			System.out.print(i+" ");
		}
		System.out.println();
	}
}