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ternary_search.cpp
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ternary_search.cpp
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#include <iostream>
#define absolutePrecision 10
#define _target 10
#define MAX 10000000 ///< Maximum length of array
void get_input() {}
int it_ternary_search(int left, int right, int A[], int target) {
while (1) {
if (left < right) {
if (right - left < absolutePrecision) {
for (int i = left; i <= right; i++)
if (A[i] == target)
return i;
return -1;
}
int oneThird = (left + right) / 3 + 1;
int twoThird = (left + right) * 2 / 3 + 1;
if (A[oneThird] == target)
return oneThird;
else if (A[twoThird] == target)
return twoThird;
else if (target > A[twoThird])
left = twoThird + 1;
else if (target < A[oneThird])
right = oneThird - 1;
else
left = oneThird + 1, right = twoThird - 1;
} else {
return -1;
}
}
}
int rec_ternary_search(int left, int right, int A[], int target) {
if (left < right) {
if (right - left < absolutePrecision) {
for (int i = left; i <= right; i++)
if (A[i] == target)
return i;
return -1;
}
int oneThird = (left + right) / 3 + 1;
int twoThird = (left + right) * 2 / 3 + 1;
if (A[oneThird] == target)
return oneThird;
if (A[twoThird] == target)
return twoThird;
if (target < A[oneThird])
return rec_ternary_search(left, oneThird - 1, A, target);
if (target > A[twoThird])
return rec_ternary_search(twoThird + 1, right, A, target);
return rec_ternary_search(oneThird + 1, twoThird - 1, A, target);
} else {
return -1;
}
}
void ternary_search(int N, int A[], int target) {
std::cout << it_ternary_search(0, N - 1, A, target) << '\t';
std::cout << rec_ternary_search(0, N - 1, A, target) << '\t';
std::cout << std::endl;
}
int main() {
int N = 21;
int A[] = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 10};
get_input();
ternary_search(N, A, _target);
return 0;
}