#include <stdio.h>
#include <math.h>
#include <stdbool.h>

float Res_cal(float a, float b, float c, float d);
float Res_cal2(float a, float b, float c);
int float_equal(float x, float y, float epsilon);
void screen1(float res);
void screen2(float res);

float arr1[32] = {0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.3, 4, 5, 6, 8, 10, 12, 15, 20, 22, 25, 30, 33, 39, 47, 50, 68, 75, 100, 120, 150, 200, 300, 330, 500};

void main() {

	float res, mistake;
	int num, flag;
	//printf("%f\n", arr1[0]);
	flag = 0;
	while (true) {
		printf("请输入需要计算的阻值(范围0.1-100)：");
		scanf("%f", &res);

		printf("请输入并联电阻个数(3或者4)：");
		scanf("%d", &num);

		for (int i = 0; i < 32; i++) {
			if (float_equal(res, arr1[i], 0.0001)) {
				printf("arr1[%d]:%g\r\n", i, arr1[i]);
				flag = 1;
				break;
			}
		}
		if ( !flag) {
			if (3 == num)
				screen1(res);
			else
				screen2(res);
		}
		flag = 0;
		printf("***********************************************************\r\n");
	}
}

float Res_cal(float a, float b, float c, float d) {
	float result;
	result = 1 / (1 / a + 1 / b + 1 / c + 1 / d);
	return result;
}

float Res_cal2(float a, float b, float c) {
	float result;
	result = 1 / (1 / a + 1 / b + 1 / c );
	return result;
}

int float_equal(float x, float y, float epsilon) {
	if (fabs(x - y) < epsilon)
		return 1;
	else
		return 0;
}

void screen2(float res) {
	int arr[4];
	float result, flag = 1;
	for (int i = 0; i < 32; i++) {
		for (int j = i; j < 32; j++) {
			for (int k = i; k < 32; k++) {
				for (int l = i; l < 32; l++) {
					if (flag > fabs(Res_cal(arr1[i], arr1[j], arr1[k], arr1[l]) - res)) {
						flag = fabs(Res_cal(arr1[i], arr1[j], arr1[k], arr1[l]) - res);
						result = Res_cal(arr1[i], arr1[j], arr1[k], arr1[l]);
						arr[0] = i;
						arr[1] = j;
						arr[2] = k;
						arr[3] = l;
					}
				}
			}
		}
	}
	printf("arr1[%d]:%g  arr1[%d]:%g arr1[%d]:%g arr1[%d]:%g 阻值：%g\r\n", arr[0], arr1[arr[0]], arr[1], arr1[arr[1]],
	       arr[2],
	       arr1[arr[2]], arr[3], arr1[arr[3]], result);
}

void screen1(float res) {
	int arr[3];
	float result, flag = 1;
	for (int i = 0; i < 32; i++) {
		for (int j = i; j < 32; j++) {
			for (int k = i; k < 32; k++) {
				if (flag > fabs(Res_cal2(arr1[i], arr1[j], arr1[k]) - res)) {
					flag = fabs(Res_cal2(arr1[i], arr1[j], arr1[k]) - res);
					result = Res_cal2(arr1[i], arr1[j], arr1[k]);
					arr[0] = i;
					arr[1] = j;
					arr[2] = k;
				}
			}
		}
	}
	printf("arr1[%d]:%g  arr1[%d]:%g arr1[%d]:%g 阻值：%g\r\n", arr[0], arr1[arr[0]], arr[1], arr1[arr[1]], arr[2],
	       arr1[arr[2]], result);
}