162 Find Peak Element
162. Find Peak Element
1. Question
A peak element is an element that is greater than its neighbors.
Given an input array wherenum[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 thatnum[-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.
2. Implementation
(1) Binary Search
class Solution {
public int findPeakElement(int[] nums) {
if (nums.length <= 1) {
return 0;
}
int start = 0, end = nums.length - 1, mid = 0;
while (start + 1 < end) {
mid = start + (end - start) / 2;
if (nums[mid - 1] < nums[mid] && nums[mid] > nums[mid + 1]) {
return mid;
}
else if (nums[mid - 1] < nums[mid] && nums[mid] < nums[mid + 1]) {
start = mid + 1;
}
else {
end = mid - 1;
}
}
return nums[start] > nums[end] ? start : end;
}
}
3. Time & Space Complexity
Binary Search: 时间复杂度O(logn), 空间复杂度O(1)
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