如何编写三元搜索算法？

Question

搜索排序的算法 n 项的列表，通过将其划分为几乎 n/3 项的三个子列表。该算法发现 可能包含给定项目的子列表并将其分成三个较小的子列表 大小相等。算法会重复这个过程，直到找到该项目或得出该项目的结论 不在列表中

Answer 1

您在那里描述的称为Ternary Searching Algorithm，它类似于二分搜索，不同之处在于我们将集合分为三个子集。以下是 C++ 的解释：

// Function to perform Ternary Search
int ternarySearch(int l, int r, int key, int ar[])
{
    if (r >= l) {
 
        // Find the mid1 and mid2
        int mid1 = l + (r - l) / 3;
        int mid2 = r - (r - l) / 3;
 
        // Check if key is present at any mid
        if (ar[mid1] == key) {
            return mid1;
        }
        if (ar[mid2] == key) {
            return mid2;
        }
 
        // Since key is not present at mid,
        // check in which region it is present
        // then repeat the Search operation
        // in that region
        if (key < ar[mid1]) {
 
            // The key lies in between l and mid1
            return ternarySearch(l, mid1 - 1, key, ar);
        }
        else if (key > ar[mid2]) {
 
            // The key lies in between mid2 and r
            return ternarySearch(mid2 + 1, r, key, ar);
        }
        else {
 
            // The key lies in between mid1 and mid2
            return ternarySearch(mid1 + 1, mid2 - 1, key, ar);
        }
    }
 
    // Key not found
    return -1;
}
 
// Driver code
int main()
{
    int l, r, p, key;
 
    // Get the array
    // Sort the array if not sorted
    int ar[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
 
    // Starting index
    l = 0;
 
    // length of array
    r = 9;
 
    // Checking for 5
 
    // Key to be searched in the array
    key = 5;
 
    // Search the key using ternarySearch
    p = ternarySearch(l, r, key, ar);
 
    // Print the result
    cout << "Index of " << key
         << " is " << p << endl;
 
    // Checking for 50
 
    // Key to be searched in the array
    key = 50;
 
    // Search the key using ternarySearch
    p = ternarySearch(l, r, key, ar);
 
    // Print the result
    cout << "Index of " << key
         << " is " << p << endl;
}