只考虑y轴轴值为0，x轴可以变化，用分治法实现：

#include <iostream>
#include <algorithm>
using namespace std;
const double Max = 201230089058;
double nearest1(double *array, double low, double high, int count);
int main() {
	int n;
	cout<<"输入x轴座标数目:";
	cin>>n;
	double *p = new double[n];
	cout<<"输入每个x轴值:";
	for(int i = 0; i < n; i++) {
		cin>>p[i];
	}
	
	sort(p, p + n);

	cout <<"最近值为 = "<<nearest1(p, p[0], p[n - 1], n) << endl;

	delete [] p;

	return 0;
}

double nearest1(double *array, double low, double high, int count) {
	// 求平均值
	
	double sum = 0.0;
	double average = 0.0;
	double dis;
	if(1 == count) {
		return Max; 
	}
	for (int i = 0; i < count; i++) {
		sum += *(array + i);
	}

	average = sum / count;
	// 将小于平均值的数和大于平均值的数
	int j = 0;
	for (; j < count; j++) {

		if ((array[j] <= average) && (array[j + 1] >= average)) {
			break;
		}
	}

	dis = array[j + 1] - array[j];
	double leftdis;
	double rightdis;
	
	leftdis = nearest1(array, array[0], array[j], j + 1);
	rightdis = nearest1(array + j + 1,array[j + 1], array[count - 1], count - j -1);

	dis = (dis <= leftdis) ? dis : leftdis;
	dis = (dis <= rightdis) ? dis : rightdis;
	return dis;
}