[LeetCode] Find Peak Element

最新推荐文章于 2024-11-13 02:34:54 发布

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本文介绍了一种寻找峰值元素的方法，峰值元素是指比其邻居大的元素。文章提供了两种解决方案，一种使用了中间值比较来逐步缩小搜索范围，另一种通过比较相邻两个元素来确定峰值的方向。

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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.

解法1

class Solution {
public:
    int findPeakElement(const vector<int> &num) {
        int len = num.size() - 1;
        int low = 0,high = len;
        if(high == 1) return num[0] > num[1] ? 0 : 1;
        while(low <= high){
            int mid = (low + high)/2;
            if(low == high) return mid;
            if(mid == 0) return num[0] > num[1] ? 0 : 1;
            if(mid == len) return num[len - 1] > num[len] ? len - 1 : len;
            if(num[mid] > num[mid - 1] && num[mid] > num[mid + 1])
                return mid;
            else if(num[mid] < num[mid - 1])
                high = mid - 1;
            else if(num[mid] < num[mid + 1])
                low = mid + 1;
        }
    }
};

解法2

class Solution {
public:
    int findPeakElement(const vector<int> &num) 
    {
        int low = 0;
        int high = num.size()-1;
        
        while(low < high)
        {
            int mid1 = (low+high)/2;
            int mid2 = mid1+1;
            if(num[mid1] < num[mid2])
                low = mid2;
            else
                high = mid1;
        }
        return low;
    }
};