Find in Mountain Array

(This problem is an interactive problem.)

You may recall that an array A is a mountain array if and only if:

• A.length >= 3
• There exists some i with 0 < i < A.length - 1 such that:
  • A[0] < A[1] < ... A[i-1] < A[i]
  • A[i] > A[i+1] > ... > A[A.length - 1]

Given a mountain array mountainArr, return the minimum index such that mountainArr.get(index) == target.  If such an index doesn't exist, return -1.

You can't access the mountain array directly.  You may only access the array using a MountainArray interface:

• MountainArray.get(k) returns the element of the array at index k (0-indexed).
• MountainArray.length() returns the length of the array.

Submissions making more than 100 calls to MountainArray.get will be judged Wrong Answer.  Also, any solutions that attempt to circumvent the judge will result in disqualification.

Example 1:

Input: array = [1,2,3,4,5,3,1], target = 3
Output: 2
Explanation: 3 exists in the array, at index=2 and index=5. Return the minimum index, which is 2.

思路：三次binary search，找到peekIndex，然後分兩段分別search。注意左右兩邊是不一樣的，要分別寫search；

/**
 * // This is MountainArray's API interface.
 * // You should not implement it, or speculate about its implementation
 * interface MountainArray {
 *     public int get(int index) {}
 *     public int length() {}
 * }
 */
 
class Solution {
    public int findInMountainArray(int target, MountainArray mountainArr) {
        int peekIndex = findPeak(mountainArr);
        int leftindex = findLeft(target, mountainArr, 0, peekIndex);
        return leftindex != -1 ? leftindex : 
        findRight(target, mountainArr, peekIndex, mountainArr.length() - 1);
    }
    
    private int findRight(int target, MountainArray mountainArr, int start, int end) {
         while(start + 1 < end) {
            int mid = start + (end - start) / 2;
            if(mountainArr.get(mid) > target) {
                start = mid;
            } else {
                // mountainArr.get(mid) <= target
                end = mid;
            }
        }
        if(mountainArr.get(start) == target) {
            return start;
        }
        if(mountainArr.get(end) == target) {
            return end;
        }
        return -1;
    }
    
    private int findLeft(int target, 
                           MountainArray mountainArr, int start, int end) {
        while(start + 1 < end) {
            int mid = start + (end - start) / 2;
            if(mountainArr.get(mid) > target) {
                end = mid;
            } else {
                // mountainArr.get(mid) <= target
                start = mid;
            }
        }
        if(mountainArr.get(start) == target) {
            return start;
        }
        if(mountainArr.get(end) == target) {
            return end;
        }
        return -1;
    }
    
    private int findPeak(MountainArray mountainArr) {
        int start = 0; int end = mountainArr.length() - 1;
        while(start + 1 < end) {
            int mid = start + (end - start) / 2;
            if(mountainArr.get(mid) > mountainArr.get(mid + 1)) {
                end = mid;
            } else {
                // mountainArr.get(mid) <= mountainArr.get(mid + 1)
                start = mid;
            }
        }
        
        if(mountainArr.get(start) > mountainArr.get(end)){
            return start;
        }
        return end;
    }
}