我正在处理一个编码问题，希望我使用二进制搜索方法来查看用户的值是否与我从文件中提取的数组中的值匹配。但是，我的二进制搜索仅将数组内的第一个数字识别为目标。
我已经动了好几个小时了，我不知道怎么了。
public static void main(String[] args) throws FileNotFoundException {
final double THRESHOLD = 0.01; //set threshold for doubles comparison
boolean done = false;
File fileName;
Scanner in = new Scanner (System.in);
Scanner user;
//prompt user to input a file
while (!done) {
System.out.print("Enter the name of the file with your investments: ");
fileName = new File(in.nextLine());
user = new Scanner (fileName);
int size = user.nextInt();
double investments [] = new double [size];
int index = 0;
while (user.hasNextDouble()) {
investments [index] = user.nextDouble();
index++;
}
//sort values into specified categories
int i = 0, aValues = 0, bValues = 0, cValues = 0, dValues = 0, fValues = 0;
while (i < investments.length) {
if (investments [i] > 1250) {
aValues++;
}
if (investments [i] > 1100 && investments [i] < 1500) {
bValues++;
}
if (investments [i] > 900 && investments [i] < 1100) {
cValues++;
}
if (investments [i] > 750 && investments [i] < 900) {
dValues++;
}
if (investments [i] > 0 && investments [i] < 750) {
fValues++;
}
i++;
}
//print table
System.out.printf("\n%-10s$%.2f", "Mean: ", getMean(investments));
System.out.printf("\n%-10s$%.2f", "Minimum", getMinimum(investments));
System.out.printf("\n%-10s$%.2f\n", "Maximum", getMaximum(investments));
System.out.printf("\n%-10s", "Number of As: " + aValues);
System.out.printf("\n%-10s", "Number of Bs: " + bValues);
System.out.printf("\n%-10s", "Number of Cs: " + cValues);
System.out.printf("\n%-10s", "Number of Ds: " + dValues);
System.out.printf("\n%-10s\n", "Number of Fs: " + fValues);
System.out.printf("\n%-10s", "Total number of investments: " + size);
System.out.printf("\n\n");
//sort array of investments and print
bubbleSort (investments);
for (double nvestments : investments) {
System.out.printf("%.3f\n", nvestments);
}
System.out.print("Would you like to search for an investment amount? (Y/N): ");
String response = in.next();
do {
if (response.equalsIgnoreCase("y")) {
System.out.print("Enter investment amount: $");
double enteredTarget = in.nextDouble();
if (THRESHOLD >= Math.abs(investments[binarySearch(investments, enteredTarget)] - enteredTarget)) {
done = false;
System.out.println(investments[binarySearch(investments, enteredTarget)] + " " + enteredTarget);
System.out.printf("Investment amount $%.2f is found at position %d\n", enteredTarget, index(investments, enteredTarget)+1);
System.out.print("Would you like to search for an investment amount? (Y/N): ");
response = in.next();
}
else {
System.out.println(investments[binarySearch(investments, enteredTarget)] + " " + enteredTarget);
System.out.printf("Investment amount $%.2f is found at position 00\n", enteredTarget);
System.out.print("Would you like to search for an investment amount? (Y/N): ");
response = in.next();
}}
else if (response.equalsIgnoreCase("n")) {
done = true;
}
} while (response.equalsIgnoreCase("y"));
}
in.close();
}
public static double getMinimum (double [] array) {
double minValue = array [0];
for (int i=1; i<array.length; i++) {
if (array [i] < minValue) {
minValue = array[i];
}
}
return minValue;
}
public static double getMaximum (double [] array) {
double maxValue = array [0];
for (int i=1; i<array.length; i++) {
if (array [i] > maxValue) {
maxValue = array[i];
}
}
return maxValue;
}
public static double getMean (double [] array) {
double sum = 0;
for (int i = 0; i < array.length; i++) {
sum = array [i] + sum;
}
double mean = sum / array.length;
return mean;
}
public static void bubbleSort (double [] array) {
boolean sorted = false;
int i = 0, j = 0;
while (!sorted) {
if (i == array.length) {
sorted = false;
}
else {
sorted = true;
for (i = 0; i < array.length-1; i++) {
for (j = 0; j < array.length-i-1; j++) {
if (array [j] < array [j+1]) {
swap (array, j, j+1);
}
}
}
}
}
}
public static void swap (double [] array, int j, int i) {
double temp = array [i];
array [i] = array [j];
array [j] = temp;
}
public static int binarySearch (double [] array, double target) {
int lb = 0;
int ub = array.length - 1;
int retVal = -1;
while (ub >= lb && retVal < 0) {
int mid = (ub + lb) / 2;
if (array [mid] < target) {
lb = mid + 1;
}
else if (array [mid] > target) {
ub = mid - 1;
}
else {
retVal = mid;
}
}
return retVal;
}
public static int index (double [] array, double target) {
int i;
final double THRESHOLD = 0.01;
for (i = 0; i < array.length; i++) {
if (Math.abs(array [i] - target) < THRESHOLD) {
return i;
}
}
return i+1;
}
}
例如，如果我的数组包含800.9、300、100、60.50、23.45和23.33，并且当我要求我输入一个值时我键入100，它将与800.9而不是其余的值进行比较。
答案 0 :(得分：2)
Binary Search仅适用于有序数组，在您的情况下，您的数组按Descending顺序排序，并且您为Binary Search实现了Ascending order算法。
您的数组：800.9, 300, 100, 60.50, 23.45, & 23.33 //降序
对于降序数组，您必须对条件运算符求逆。
if (array [mid] > target) {
lb = mid + 1;
}
else if (array [mid] < target) {
ub = mid - 1;
}
else {
retVal = mid;
}