Given an array, print the Next Greater Element (NGE) for every element. The Next greater Element for an element x is the first greater element on the right side of x in array. Elements for which no greater element exist, consider next greater element as -1. The next greater elements should be printed in same order as input array.
Input : arr = [4, 5, 2, 25}
Output : 5 25 25 -1
Input : arr = [4, 5, 2, 25, 10}
Output : 5 25 25 -1 -1
We have discussed a solution here that does not print same order. Here we traverse array from rightmost element.
In this approach we have started iterating from the last element(nth) to the first(1st) element
The benefit is that when we arrive at a certain index his next greater element will be already in stack and we can directly get this element while at the same index.
- After reaching a certain index we will pop the stack till we get the greater element on top from the current element and that element will be the answer for current element
- If stack gets empty while doing the pop operation then the answer would be -1
Then we will stored the answer in an array for the current index.
Below is the implementation of above approach:
# A Stack based Python3 program to find next
# greater element for all array elements
# in same order as input.
# prints element and NGE pair for all
# elements of arr of size n
def printNGE(arr, n):
s = list()
arr1 = [0 for i in range(n)]
# iterating from n-1 to 0
for i in range(n – 1, -1, -1):
# We will pop till we get the greater
# element on top or stack gets empty
while (len(s) > 0 and s[-1] < arr[i]): s.pop() # if stack gots empty means there # is no element on right which is # greater than the current element. # if not empty then the next greater # element is on top of stack if (len(s) == 0): arr1[i] = -1 else: arr1[i] = s[-1] s.append(arr[i]) for i in range(n): print(arr[i], " ---> “, arr1[i] )
# Driver Code
arr = [ 11, 13, 21, 3 ]
n = len(arr)
# This code is contributed by Mohit kumar 29
11 -- 13 13 -- 21 21 -- -1 3 -- -1
Time Complexity: O(n)
Auxiliary Space: O(n) There is no extra space required if you want to print the next greater of each element in reverse order of input(means first, for the last element and then for second last and so on till the first element)
- Longest Subarray with first element greater than or equal to Last element
- Replace every element with the least greater element on its right
- Next Greater Element
- Previous greater element
- Next Greater Frequency Element
- Smallest Greater Element on Right Side
- Find the element before which all the elements are smaller than it, and after which all are greater
- Elements greater than the previous and next element in an Array
- Find closest greater value for every element in array
- Count of subarrays whose maximum element is greater than k
- Rearrange an array such that every odd indexed element is greater than it previous
- Closest greater or same value on left side for every element in array
- First strictly greater element in a sorted array in Java
- Sum of elements in an array with frequencies greater than or equal to that element
- Adding elements of an array until every element becomes greater than or equal to k
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.