Find Peak Element
Problem:
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.
Analysis:
if (nums[m - 1] < nums[m] < nums[m+1]) peak is on right
if (nums[m - 1] > nums[m] > nums[m+1]) peak is on left
Solution:
Return whichever is larger.
class Solution { public int findPeakElement(int[] nums) { int left = 0, right = nums.length - 1; while (left+ 1< right) { int mid = left+ (right - left)/2; if (nums[mid] > nums[mid + 1]){ right = mid; } else { left = mid; } } return nums[left] > nums[right] ? left: right; } }
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