TriSortedArray

#include <iostream>

using namespace std;

int A[] = {1, 3, 8, 12, 9, 7, 2, 4, 6}, Size = 0; // Will update size in main

// Get the first transition index
int findTransition1() {
    int left = 0, right = Size - 1;

    while (left < right) {
        int mid = left + (right - left) / 2;

        if (A[mid] > A[mid + 1]) {
            right = mid; // Move to left subarray
        } else {
            left = mid + 1; // Move to right subarray
        }
    }

    return left;
}

// Get the second transition index
int findTransition2() {
    int left = 0, right = Size - 1;

    while (left < right) {
        int mid = left + (right - left) / 2;

        if (A[mid] < A[mid + 1]) {
            right = mid; // Move to left subarray
        } else {
            left = mid + 1; // Move to right subarray
        }
    }

    return left;
}

// Binary Search on increasing subarray
int increasingBinarySearch(int left, int right, int x) {
    while (left <= right) {
        int mid = left + (right - left) / 2;

        if (A[mid] == x)
            return mid;
        if (A[mid] < x)
            left = mid + 1;
        else
            right = mid - 1;
    }

    return -1;
}

// Binary Search on decreasing subarray
int decreasingBinarySearch(int left, int right, int x) {
    while (left <= right) {
        int mid = left + (right - left) / 2;

        if (A[mid] == x)
            return mid;
        if (A[mid] > x)
            left = mid + 1;
        else
            right = mid - 1;
    }

    return -1;
}

// Function to search x in a TriSorted array
int triSortedArraySearch(int x) {
    int transition1 = findTransition1(), transition2 = findTransition2();
    cout<<"Transition Indices: "<<transition1<<" "<<transition2<<endl;

    // Search in the increasing part 1
    int result = increasingBinarySearch(0, transition1-1, x);
    if (result != -1)
        return result ;
    // Search in the decreasing part
    result = decreasingBinarySearch(transition1, transition2-1, x);
    if(result != -1)
        return result;
    // Search in the increasing part 2
    result = increasingBinarySearch(transition2, Size-1, x);
    return result;

}

int main() {

    Size = sizeof(A) / sizeof(A[0]);
    int x = 9;
    int result = triSortedArraySearch(x);
    if (result != -1) {
        cout << "Element " << x << " found at index " << result << endl;
    } else {
        cout << "Element " << x << " not found." << endl;
    }

    return 0;
}