An element is a peak element if it is greater than or equal to its four neighbors, left, right, top and bottom. For example neighbors for A[i][j] are A[i-1][j], A[i+1][j], A[i][j-1] and A[i][j+1]. For corner elements, missing neighbors are considered of negative infinite value.
Input : 10 20 15 21 30 14 7 16 32 Output : 30 30 is a peak element because all its neighbors are smaller or equal to it. 32 can also be picked as a peak. Input : 10 7 11 17 Output : 17
Below are some facts about this problem:
1: A Diagonal adjacent is not considered as neighbor.
2: A peak element is not necessarily the maximal element.
3: More than one such elements can exist.
4: There is always a peak element. We can see this property by creating some matrices using pen and paper.
Method 1: (Brute Force)
Iterate through all the elements of Matrix and check if it is greater/equal to all its neighbors. If yes, return the element.
Time Complexity: O(rows * columns)
Auxiliary Space: O(1)
Method 2 : (Efficient)
This problem is mainly an extension of Find a peak element in 1D array. We apply similar Binary Search based solution here.
- Consider mid column and find maximum element in it.
- Let index of mid column be ‘mid’, value of maximum element in mid column be ‘max’ and maximum element be at ‘mat[max_index][mid]’.
- If max >= A[index][mid-1] & max >= A[index][pick+1], max is a peak, return max.
- If max < mat[max_index][mid-1], recur for left half of matrix.
- If max < mat[max_index][mid+1], recur for right half of matrix.
Below is the implementation of above algorithm:
Time Complexity : O(rows * log(columns)). We recur for half the number of columns. In every recursive call, we linearly search for the maximum in the current mid column.
Auxiliary Space: O(columns/2) for Recursion Call Stack
This article is contributed by Rohit Thapliyal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
- Find a peak element
- Find if array has an element whose value is half of array sum
- Find an element in Bitonic array
- Program to find largest element in an array
- Find the element that appears once in a sorted array
- Find first and last positions of an element in a sorted array
- Find the index of an array element in Java
- Find the minimum element in a sorted and rotated array
- Find the maximum element in an array which is first increasing and then decreasing
- Given an array and two integers l and r, find the kth largest element in the range [l, r]
- Python heapq to find K'th smallest element in a 2D array
- Find the only repeating element in a sorted array of size n
- Find missing element in a sorted array of consecutive numbers
- Find index of an extra element present in one sorted array
- Find frequency of each element in a limited range array in less than O(n) time