How to use binary search algorithm in C++

How to use the binary search algorithm in C

The binary search algorithm (Binary Search) is an efficient search algorithm that divides an ordered data set into Both halves search in the middle position of the data set each time. By comparing the value in the middle position with the target value, the search range is continuously narrowed until the target value is found or the target value is determined not to exist. The following will introduce how to use the binary search algorithm in C and give specific code examples.

1. Determine the search scope
   Before using the binary search algorithm, you first need to make sure that the data set to be searched is ordered. For example, we have an ordered array of integers nums in which we want to search for a certain target value target.
2. Define binary search function
   In C, we can define a function to implement the binary search algorithm. The input parameters of this function include the array to be searched, the starting and ending positions of the array, and the target value target. The return value of the function is the index of the target value in the array. If the target value does not exist, a specific value (such as -1) can be returned.

The specific function definition is as follows:

int binarySearch(int nums[], int start, int end, int target) {
    // 定义二分搜索的起始位置和结束位置
    int left = start;
    int right = end;
    
    while (left <= right) {
        // 计算中间位置
        int mid = left + (right - left) / 2;
        
        // 如果中间位置的值等于目标值，直接返回索引
        if (nums[mid] == target) {
            return mid;
        }
        
        // 如果中间位置的值大于目标值，更新结束位置
        else if (nums[mid] > target) {
            right = mid - 1;
        }
        
        // 如果中间位置的值小于目标值，更新起始位置
        else {
            left = mid + 1;
        }
    }
    
    // 目标值不存在，返回-1
    return -1;
}

3. Calling the binary search function
   By calling the binary search function, we can get the index of the target value in the array. For example, we have an ordered array nums and we want to search for the target value target. You can use the following code to call the binary search function:

int nums[] = {1, 3, 5, 7, 9};
int n = sizeof(nums) / sizeof(nums[0]);
int target = 5;
int index = binarySearch(nums, 0, n - 1, target);

if (index != -1) {
    cout << "目标值的索引为：" << index << endl;
}
else {
    cout << "目标值不存在！" << endl;
}

In the above code, we first define an ordered array nums, and then calculate the length n of the array. Then the target value target is defined, and the binary search function binarySearch is called to search the index of the target value. Finally, the output is based on the result returned by the function.

Through the above steps, we can use the binary search algorithm in C to perform efficient search operations. In actual applications, the binary search function can be called according to specific scenarios and requirements, and further processing can be performed based on the returned results.

Summary
The binary search algorithm is an efficient search algorithm suitable for ordered data collections. In C, we can search by defining a binary search function and passing in the array to be searched, the starting position, the ending position and the target value. By continuously updating the search range, the index of the target value can eventually be found. We hope that the introduction and code examples in this article can help readers better understand and apply the binary search algorithm.

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