如何编写三元查找算法?

Question

搜索排序将n个项目的列表分成三个子列表，每个子列表几乎有n/3个项目。这个算法找到子列表，该子列表可能包含给定的项，并将其分为三个更小的子列表相同的大小。算法重复此过程，直到找到该项或得出该项的结论不在列表中

Answer 1

你所描述的称为Ternary Searching Algorithm，它类似于二分查找，除了我们将集合分为三个子集。下面是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;
}