Problem no. 33.java

// Ques : Search in Rotated Sorted Array
// Ques Link : https://leetcode.com/problems/search-in-rotated-sorted-array/ 

package com.nitin;

public class RBS {
    public static void main(String[] args) {
        int[] arr = {4,5,6,7,0,1,2};
        int target = 5;
        System.out.println(search(arr, target));
    }

    static int search(int[] nums, int target) {
        int pivot = findPivot(nums);

        // if did not find a pivot, it means the array is not rotated
        if (pivot == -1){
            // just do normal binary search
            return binarySearch(nums, target, 0, nums.length - 1);

        }

        // if pivot is found, you have found 2 asc sorted arrays
        if (nums[pivot] == target) {
            return pivot;
        }

        if (target >= nums[0]) {
            return binarySearch(nums, target, 0, pivot - 1);
        }

        return binarySearch(nums, target, pivot + 1, nums.length - 1);
    }

    static int binarySearch(int[] arr, int target, int start, int end) {

        while(start <= end) {
            // find the middle element
//            int mid = (start + end) / 2; // might be possible that the (start + end) exceeds the range of int in java
            int mid = start + (end - start) / 2;

            if (target < arr[mid]) {
                end = mid - 1;
            } else if (target > arr[mid]) {
                start = mid + 1;
            } else {
                // ans found
                return mid;
            }
        }
        return -1;
    }

    // this will not work for duplicate value
    static int findPivot(int[] arr){
        int start = 0;
        int end = arr.length - 1;
        while (start <=end) {
            int mid = start + (end - start) / 2;
            // 4 cases over here
            if (mid < end && arr[mid] > arr[mid + 1]) {
                return mid;
            }
            if (mid > start && arr[mid] < arr[mid - 1]) {
                return mid - 1;
            }
            if (arr[mid] <= arr[start]) {
                end = mid - 1;
            } else {
                start = mid  + 1;
            }
        }
        return - 1;
    }
}