[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。文章提供了三种不同的C++实现方式，包括遍历查找和使用二分查找算法来提高效率。

From : https://leetcode.com/problems/decode-ways/

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.

class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        int n = nums.size();
        if(n == 1) return 0;
        if(nums[0] > nums[1]) return 0;
        if(nums[n-1] > nums[n-2]) return n-1;
        for(int i = 1; i < n-1; i ++)
            if(nums[i] > nums[i-1] && nums[i] > nums[i+1])
                return i;
        return -1;
    }
};

public class Solution {
    public int findPeakElement(int[] nums) {
        if(nums == null || nums.length == 0) {
            return 0;
        }
        int l1 = nums.length-1, i=0;
        while(i < l1) {
            if(nums[i] > nums[i+1]) {
                break;
            }
            ++i;
        }
        return i;
    }
}

public class Solution {
    public int findPeakElement(int[] nums) {
		if (nums == null || nums.length == 0) {
			return 0;
		}
		return find(nums, 0, nums.length - 1);
	}

	private int find(int[] nums, int low, int high) {
		if (low == high) {
			return low;
		}
		int mid = (high + low) >> 1;
		if (nums[mid] > nums[mid + 1]) {
			return find(nums, low, mid);
		} else {
			return find(nums, mid + 1, high);
		}
	}
}