162. Find Peak Element(unsolved)

最新推荐文章于 2021-01-09 09:50:36 发布

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本文介绍了一种高效的算法来寻找数组中的峰值元素。峰值元素是指比其邻居大的元素。通过使用折半查找方法，可以在O(log n)的时间复杂度内找到一个峰值元素的索引。

A peak element is an element that is greater than its neighbors.

Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that num[-1] = num[n] = -∞.

For example, in array [1, 2, 3, 1], 3 is a peak element and your function should return the index number 2.

解答：
就是折半查找就好了。关键在于边界条件的选定。可以考虑
left=mid 或者left=mid+1。返回可以是right，或者mid 或者left;这个都得跑test case确定

class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        if(nums.size()==1) return 0;
        int left=0;
        int right=nums.size()-1;
        int mid=0;
        while(left<right)
        {
            mid=(left+right)/2;
            if(nums[mid]<nums[mid+1]) left=mid+1;
            else right=mid;
        }
        return right;
    }
};