Maximum Number in Mountain Sequence

Description

Given a mountain sequence of nintegers 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

Related problems

Find Peak Element

Implementation

Link: http://lintcode.com/en/problem/maximum-number-in-mountain-sequence/

class Solution {
public:
    /**
     * @param nums a mountain sequence which increase firstly and then decrease
     * @return then mountain top
     */
    int mountainSequence(vector<int>& nums) {
        // Write your code here
        if(nums.size() == 0 ) return -1;

        int start = 0, end = nums.size() - 1;

        while(start + 1 < end) {
            int mid = start + (end - start) / 2;
            if(nums[mid] < nums[mid - 1]) {
                end = mid;
            } else {
                start = mid;
            }
        }

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

    int mountainSequenceVersion2(vector<int>& nums) {
        // Write your code here
        if(nums.size() == 0 ) return -1;

        int start = 0, end = nums.size() - 1;

        while(start + 1 < end) {
            int mid = start + (end - start) / 2;
            if(nums[mid] > nums[mid + 1]) {
                end = mid;
            } else {
                start = mid;
            }
        }

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