英文:
Integer variable stores 0 as method return value
问题
在Java中，我试图使用递归程序执行二分搜索，算法似乎完全正确，但我从递归函数中存储结果的变量却将值存储为0。
在以下代码中，我想将找到的元素的索引存储在变量result中，但输出将result的值打印为0。
当我在返回语句之前打印mid的值时，该值是正确的。如何解决这个问题？
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n;
System.out.println("Enter the number of elements in the array: ");
n = scanner.nextInt();
int arr[] = new int[n];
System.out.println("Enter the array elements (from index 0): ");
for (int i = 0; i < n; i++) {
arr[i] = scanner.nextInt();
}
int ele;
System.out.println("Enter the element to be searched: ");
ele = scanner.nextInt();
/*************************************************************************************/
int result = binarySearchRecursive(arr, 0, n - 1, ele);
System.out.println(result);
/************************************************************************************/
if (result == -1) {
System.out.println(ele + " not found");
} else {
System.out.println(ele + " found at index: " + result);
}
}
//Algorithm
public static int binarySearchRecursive(int arr[], int l, int r, int ele) {
//检查是否存在单个元素
if (l == r) {
if (arr[l] == ele) {
return l;
} else {
return -1;
}
} else { //多个元素
int mid = (l + r) / 2;
//检查条件
if (ele == arr[mid]) {
System.out.println("Method return 'mid' value: " + mid);
return mid;
} else if (ele < arr[mid]) {
return binarySearchRecursive(arr, l, mid - 1, ele);
} else {
return binarySearchRecursive(arr, mid + 1, r, ele);
}
}
}
}
输出在这里：输出图片
英文:
I was trying Binary Search recursive program in Java, the algorithm seems to be perfectly fine, but the variable in which I store the result from the recursive function, is storing 0 as the value.
In the following code, I want to store the index of the element found in the variable result, but the output prints result's value as 0.
When I print the value of mid before the return statement, the value is correct. How to fix this problem??
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n;
System.out.println("Enter the number of elements in the array: ");
n = scanner.nextInt();
int arr[] = new int[n];
System.out.println("Enter the array elements (from index 0): ");
for (int i = 0; i < n; i++) {
arr[i] = scanner.nextInt();
}
int ele;
System.out.println("Enter the element to be searched: ");
ele = scanner.nextInt();
/*************************************************************************************/
int result = binarySearchRecursive(arr, 0, n - 1, ele);
System.out.println(result);
/************************************************************************************/
if (result == -1) {
System.out.println(ele + " not found");
} else {
System.out.println(ele + " found at index: " + result);
}
}
//Algorithm
public static int binarySearchRecursive(int arr[], int l, int r, int ele) {
//Check whether a single element is present
if (l == r) {
if (arr[l] == ele) {
return l;
} else {
return -1;
}
} else { //Multiple elements
int mid = (l + r) / 2;
//Check conditions
if (ele == arr[mid]) {
System.out.println("Method return 'mid' value: "+mid);
return mid;
} else if (ele < arr[mid]) {
binarySearchRecursive(arr, l, mid - 1, ele);
} else {
binarySearchRecursive(arr, mid + 1, r, ele);
}
}
return -l;
}
}
答案1
得分: 6
你应该返回递归调用的值：
if (ele == arr[mid]) {
System.out.println("方法返回 'mid' 值：" + mid);
return mid;
} else if (ele < arr[mid]) {
return binarySearchRecursive(arr, l, mid - 1, ele);
} else {
return binarySearchRecursive(arr, mid + 1, r, ele);
}
英文:
You should return the value of the recursive calls:
if (ele == arr[mid]) {
System.out.println("Method return 'mid' value: "+mid);
return mid;
} else if (ele < arr[mid]) {
return binarySearchRecursive(arr, l, mid - 1, ele);
} else {
return binarySearchRecursive(arr, mid + 1, r, ele);
}
答案2
得分: 0
你需要在binarySearchRecursive的递归函数调用中添加return语句。目前你的代码总是会落到最后的return语句，它只会返回 -l => 这会导致在binarySearchRecursive(arr, 0, n - 1, ele)中返回 0。
return binarySearchRecursive(arr, l, mid - 1, ele);
return binarySearchRecursive(arr, mid + 1, r, ele);
英文:
You have to add return statements to the recursive function calls of binarySearchRecursive. Right now your code is always falling through to the last return statement which just returns -l => which returns 0 for binarySearchRecursive(arr, 0, n - 1, ele);
return binarySearchRecursive(arr, l, mid - 1, ele);
return binarySearchRecursive(arr, mid + 1, r, ele);
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