Maximum Number in Mountain Sequence

lintcode

Given a mountain sequence of n integers which increase firstly and then decrease, find the mountain top.

Example

Given nums = [1, 2, 4, 8, 6, 3] return 8
Given nums = [10, 9, 8, 7], return 10

思路

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.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] && nums[mid] > nums[mid] + 1) {
                return nums[mid];
            } else if (nums[mid] <= nums[mid + 1]) {
                start = mid;
            } else if (nums[mid] > nums[mid + 1]) {
                end = mid;
            }
        }

        return nums[start] > nums[end] ? nums[start] : nums[end];
    }
}