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();
}
}