题目：

题解：

class Solution {
public:int findPeakElement(vector<int>& nums) {int n = nums.size();// 辅助函数，输入下标 i，返回一个二元组 (0/1, nums[i])// 方便处理 nums[-1] 以及 nums[n] 的边界情况auto get = [&](int i) -> pair<int, int> {if (i == -1 || i == n) {return {0, 0};}return {1, nums[i]};};int left = 0, right = n - 1, ans = -1;while (left <= right) {int mid = (left + right) / 2;if (get(mid - 1) < get(mid) && get(mid) > get(mid + 1)) {ans = mid;break;}if (get(mid) < get(mid + 1)) {left = mid + 1;}else {right = mid - 1;}}return ans;}
};