585. 산맥 서열 중 최대치

코드

public class Solution {
    /**
     * @param nums a mountain sequence which increase firstly and then decrease
     * @return then mountain top
     */
    public int mountainSequence(int[] nums) {
        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;
            /*          
             *     nums[mid] < nums[mid - 1]  nums[mid] < nums[mid + 1];
             *   mid     ，start end    ，   
             *     if               
             *                     
             */
            //   mid     ，                      
            if (nums[mid] > nums[mid - 1]) {
                start = mid;
            }
            if (nums[mid] > nums[mid + 1]) {
                end = mid;
            }
            //        ;        
        }
        return Math.max(nums[start], nums[end]);
    }
}

// version 2:          ，    2  ，      
public class Solution {
    /**
     * @param nums a mountain sequence which increase firstly and then decrease
     * @return then mountain top
     */
    public int mountainSequence(int[] nums) {
        int left = 0, right = nums.length - 1;
        while (left + 1 < right) {
            int m1 = left + (right - left) / 2;
            int m2 = right - (right - m1) / 2;
            if (nums[m1] < nums[m2]) {
                left = m1 + 1;
            } else if (nums[m1] > nums[m2]) {
                right = m2 - 1;
            } else {
                left = m1;
                right = m2;
            }
        }
        return nums[left] > nums[right] ? nums[left] : nums[right];
    }
}