Maximum Number in Mountain Sequence

Given a mountain sequence of 

n

 integers which increase firstly and then decrease, find the mountain top.

Example

Example 1:

Input: nums = [1, 2, 4, 8, 6, 3] 
Output: 8
           

Example 2:

Input: nums = [10, 9, 8, 7], 
Output: 10
           

思路： 就是兩邊往中間走，最後判斷start和end即可，按照九章的模闆寫萬無一失；

public class Solution {
    /**
     * @param nums: a mountain sequence which increase firstly and then decrease
     * @return: then mountain top
     */
    public int mountainSequence(int[] nums) {
        // write your code here
        if(nums == null || nums.length == 0) {
            return -1;
        }
        
        int start = 0; int end = nums.length - 1;
        while(start + 1 < end) {
            int mid = start + (end - start) / 2;
            if(nums[mid] < nums[mid+1]) {
                start = mid;
            } else { // nums[mid] > nums[mid+1];
                end = mid;
            }
        }
        
        if(nums[start] > nums[end]) {
            return nums[start];
        }
        return nums[end];
    }
}