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 the array. Elements for which no greater element exist, consider the next greater element as -1.
Example:
Input: arr[] = [ 4 , 5 , 2 , 25 ]
Output: 4 –> 5
5 –> 25
2 –> 25
25 –> -1
Explanation: except 25 every element has an element greater than them present on the right sideInput: arr[] = [ 13 , 7, 6 , 12 ]
Output: 13 –> -1
7 –> 12
6 –> 12
12 –> -1
Explanation: 13 and 12 don’t have any element greater than them present on the right side
The idea is to use two loops , The outer loop picks all the elements one by one. The inner loop looks for the first greater element for the element picked by the outer loop. If a greater element is found then that element is printed as next, otherwise, -1 is printed.
Follow the steps mentioned below to implement the idea:
-
Traverse the array from index 0 to end.
-
For each element start another loop from index i+1 to end.
- If a greater element is found in the second loop then print it and break the loop, else print -1.
-
For each element start another loop from index i+1 to end.
Below is the implementation of the above approach:
// Simple C++ program to print // next greater elements in a // given array #include <iostream> using namespace std;
/* prints element and NGE pair for all elements of arr[] of size n */ void printNGE( int arr[], int n)
{ int next, i, j;
for (i = 0; i < n; i++) {
next = -1;
for (j = i + 1; j < n; j++) {
if (arr[i] < arr[j]) {
next = arr[j];
break ;
}
}
cout << arr[i] << " --> " << next << endl;
}
} // Driver Code int main()
{ int arr[] = { 11, 13, 21, 3 };
int n = sizeof (arr) / sizeof (arr[0]);
printNGE(arr, n);
return 0;
} // This code is contributed // by Akanksha Rai(Abby_akku) |
// Simple C program to print next greater elements // in a given array #include <stdio.h> /* prints element and NGE pair for all elements of arr[] of size n */ void printNGE( int arr[], int n)
{ int next, i, j;
for (i = 0; i < n; i++) {
next = -1;
for (j = i + 1; j < n; j++) {
if (arr[i] < arr[j]) {
next = arr[j];
break ;
}
}
printf ( "%d -- %dn" , arr[i], next);
}
} int main()
{ int arr[] = { 11, 13, 21, 3 };
int n = sizeof (arr) / sizeof (arr[0]);
printNGE(arr, n);
return 0;
} |
// Simple Java program to print next // greater elements in a given array class Main {
/* prints element and NGE pair for
all elements of arr[] of size n */
static void printNGE( int arr[], int n)
{
int next, i, j;
for (i = 0 ; i < n; i++) {
next = - 1 ;
for (j = i + 1 ; j < n; j++) {
if (arr[i] < arr[j]) {
next = arr[j];
break ;
}
}
System.out.println(arr[i] + " -- " + next);
}
}
public static void main(String args[])
{
int arr[] = { 11 , 13 , 21 , 3 };
int n = arr.length;
printNGE(arr, n);
}
} |
# Function to print element and NGE pair for all elements of list def printNGE(arr):
for i in range ( 0 , len (arr), 1 ):
next = - 1
for j in range (i + 1 , len (arr), 1 ):
if arr[i] < arr[j]:
next = arr[j]
break
print ( str (arr[i]) + " -- " + str ( next ))
# Driver program to test above function arr = [ 11 , 13 , 21 , 3 ]
printNGE(arr) # This code is contributed by Sunny Karira |
// Simple C# program to print next // greater elements in a given array using System;
class GFG {
/* prints element and NGE pair for
all elements of arr[] of size n */
static void printNGE( int [] arr, int n)
{
int next, i, j;
for (i = 0; i < n; i++) {
next = -1;
for (j = i + 1; j < n; j++) {
if (arr[i] < arr[j]) {
next = arr[j];
break ;
}
}
Console.WriteLine(arr[i] + " -- " + next);
}
}
// driver code
public static void Main()
{
int [] arr = { 11, 13, 21, 3 };
int n = arr.Length;
printNGE(arr, n);
}
} // This code is contributed by Sam007 |
<script> // Simple JavaScript program to print
// next greater elements in a
// given array
/* prints element and NGE pair
for all elements of arr[] of size n */
function printNGE(arr, n)
{
var next, i, j;
for (i = 0; i < n; i++)
{
next = -1;
for (j = i + 1; j < n; j++)
{
if (arr[i] < arr[j])
{
next = arr[j];
break ;
}
}
document.write(arr[i] + " -- " + next);
document.write( "<br>" );
}
}
// Driver Code
var arr = [11, 13, 21, 3];
var n = arr.length;
printNGE(arr, n);
// This code is contributed by rdtank.
</script>
|
<?php // Simple PHP program to print next // greater elements in a given array /* prints element and NGE pair for all elements of arr[] of size n */
function printNGE( $arr , $n )
{ for ( $i = 0; $i < $n ; $i ++)
{
$next = -1;
for ( $j = $i + 1; $j < $n ; $j ++)
{
if ( $arr [ $i ] < $arr [ $j ])
{
$next = $arr [ $j ];
break ;
}
}
echo $arr [ $i ]. " -- " . $next . "\n" ;
}
} // Driver Code
$arr = array (11, 13, 21, 3);
$n = count ( $arr );
printNGE( $arr , $n );
// This code is contributed by Sam007 ?> |
11 --> 13 13 --> 21 21 --> -1 3 --> -1
Time Complexity: O(N2)
Auxiliary Space: O(1)
Find Next Greater Element using Stack:
The idea is to store the elements for which we have to find the next greater element in a stack and while traversing the array, if we find a greater element, we will pair it with the elements from the stack till the top element of the stack is less than the current element.
illustration:
Below is the illustration of the above approach:
Follow the steps mentioned below to implement the idea:
- Push the first element to stack.
-
Pick the rest of the elements one by one and follow the following steps in the loop.
- Mark the current element as next.
- If the stack is not empty, compare top most element of stack with next.
- If next is greater than the top element, Pop element from the stack. next is the next greater element for the popped element.
- Keep popping from the stack while the popped element is smaller than next. next becomes the next greater element for all such popped elements.
- Finally, push the next in the stack.
- After the loop in step 2 is over, pop all the elements from the stack and print -1 as the next element for them.
Below is the implementation of the above approach:
// A Stack based C++ program to find next // greater element for all array elements. #include <bits/stdc++.h> using namespace std;
/* prints element and NGE pair for all elements of arr[] of size n */ void printNGE( int arr[], int n)
{ stack< int > s;
/* push the first element to stack */
s.push(arr[0]);
// iterate for rest of the elements
for ( int i = 1; i < n; i++) {
if (s.empty()) {
s.push(arr[i]);
continue ;
}
/* if stack is not empty, then
pop an element from stack.
If the popped element is smaller
than next, then
a) print the pair
b) keep popping while elements are
smaller and stack is not empty */
while (s.empty() == false && s.top() < arr[i]) {
cout << s.top() << " --> " << arr[i] << endl;
s.pop();
}
/* push next to stack so that we can find
next greater for it */
s.push(arr[i]);
}
/* After iterating over the loop, the remaining
elements in stack do not have the next greater
element, so print -1 for them */
while (s.empty() == false ) {
cout << s.top() << " --> " << -1 << endl;
s.pop();
}
} /* Driver code */ int main()
{ int arr[] = { 11, 13, 21, 3 };
int n = sizeof (arr) / sizeof (arr[0]);
printNGE(arr, n);
return 0;
} |
// A Stack based C program to find next // greater element for all array elements. #include <stdbool.h> #include <stdio.h> #include <stdlib.h> #define STACKSIZE 100 // stack structure struct stack {
int top;
int items[STACKSIZE];
}; // Stack Functions to be used by printNGE() void push( struct stack* ps, int x)
{ if (ps->top == STACKSIZE - 1) {
printf ( "Error: stack overflown" );
getchar ();
exit (0);
}
else {
ps->top += 1;
int top = ps->top;
ps->items[top] = x;
}
} bool isEmpty( struct stack* ps)
{ return (ps->top == -1) ? true : false ;
} int pop( struct stack* ps)
{ int temp;
if (ps->top == -1) {
printf ( "Error: stack underflow n" );
getchar ();
exit (0);
}
else {
int top = ps->top;
temp = ps->items[top];
ps->top -= 1;
return temp;
}
} /* prints element and NGE pair for all elements of arr[] of size n */ void printNGE( int arr[], int n)
{ int i = 0;
struct stack s;
s.top = -1;
int element, next;
/* push the first element to stack */
push(&s, arr[0]);
// iterate for rest of the elements
for (i = 1; i < n; i++) {
next = arr[i];
if (isEmpty(&s) == false ) {
// if stack is not empty, then pop an element
// from stack
element = pop(&s);
/* If the popped element is smaller than next,
then a) print the pair b) keep popping while
elements are smaller and stack is not empty
*/
while (element < next) {
printf ( "n %d --> %d" , element, next);
if (isEmpty(&s) == true )
break ;
element = pop(&s);
}
/* If element is greater than next, then push
the element back */
if (element > next)
push(&s, element);
}
/* push next to stack so that we can find
next greater for it */
push(&s, next);
}
/* After iterating over the loop, the remaining
elements in stack do not have the next greater
element, so print -1 for them */
while (isEmpty(&s) == false ) {
element = pop(&s);
next = -1;
printf ( "n %d --> %d" , element, next);
}
} /* Driver code */ int main()
{ int arr[] = { 11, 13, 21, 3 };
int n = sizeof (arr) / sizeof (arr[0]);
printNGE(arr, n);
getchar ();
return 0;
} |
// Java program to print next // greater element using stack public class NGE {
static class stack {
int top;
int items[] = new int [ 100 ];
// Stack functions to be used by printNGE
void push( int x)
{
if (top == 99 ) {
System.out.println( "Stack full" );
}
else {
items[++top] = x;
}
}
int pop()
{
if (top == - 1 ) {
System.out.println( "Underflow error" );
return - 1 ;
}
else {
int element = items[top];
top--;
return element;
}
}
boolean isEmpty()
{
return (top == - 1 ) ? true : false ;
}
}
/* prints element and NGE pair for
all elements of arr[] of size n */
static void printNGE( int arr[], int n)
{
int i = 0 ;
stack s = new stack();
s.top = - 1 ;
int element, next;
/* push the first element to stack */
s.push(arr[ 0 ]);
// iterate for rest of the elements
for (i = 1 ; i < n; i++) {
next = arr[i];
if (s.isEmpty() == false ) {
// if stack is not empty, then
// pop an element from stack
element = s.pop();
/* If the popped element is smaller than
next, then a) print the pair b) keep
popping while elements are smaller and
stack is not empty */
while (element < next) {
System.out.println(element + " --> "
+ next);
if (s.isEmpty() == true )
break ;
element = s.pop();
}
/* If element is greater than next, then
push the element back */
if (element > next)
s.push(element);
}
/* push next to stack so that we can find next
greater for it */
s.push(next);
}
/* After iterating over the loop, the remaining
elements in stack do not have the next greater
element, so print -1 for them */
while (s.isEmpty() == false ) {
element = s.pop();
next = - 1 ;
System.out.println(element + " -- " + next);
}
}
// Driver Code
public static void main(String[] args)
{
int arr[] = { 11 , 13 , 21 , 3 };
int n = arr.length;
printNGE(arr, n);
}
} // Thanks to Rishabh Mahrsee for contributing this code |
# Python program to print next greater element using stack # Stack Functions to be used by printNGE() def createStack():
stack = []
return stack
def isEmpty(stack):
return len (stack) = = 0
def push(stack, x):
stack.append(x)
def pop(stack):
if isEmpty(stack):
print ( "Error : stack underflow" )
else :
return stack.pop()
'''prints element and NGE pair for all elements of arr[] '''
def printNGE(arr):
s = createStack()
element = 0
next = 0
# push the first element to stack
push(s, arr[ 0 ])
# iterate for rest of the elements
for i in range ( 1 , len (arr), 1 ):
next = arr[i]
if isEmpty(s) = = False :
# if stack is not empty, then pop an element from stack
element = pop(s)
'''If the popped element is smaller than next, then
a) print the pair
b) keep popping while elements are smaller and
stack is not empty '''
while element < next :
print ( str (element) + " -- " + str ( next ))
if isEmpty(s) = = True :
break
element = pop(s)
'''If element is greater than next, then push
the element back '''
if element > next :
push(s, element)
'''push next to stack so that we can find
next greater for it '''
push(s, next )
'''After iterating over the loop, the remaining
elements in stack do not have the next greater
element, so print -1 for them '''
while isEmpty(s) = = False :
element = pop(s)
next = - 1
print ( str (element) + " -- " + str ( next ))
# Driver code arr = [ 11 , 13 , 21 , 3 ]
printNGE(arr) # This code is contributed by Sunny Karira |
using System;
// c# program to print next // greater element using stack public class NGE {
public class stack {
public int top;
public int [] items = new int [100];
// Stack functions to be used by printNGE
public virtual void push( int x)
{
if (top == 99) {
Console.WriteLine( "Stack full" );
}
else {
items[++top] = x;
}
}
public virtual int pop()
{
if (top == -1) {
Console.WriteLine( "Underflow error" );
return -1;
}
else {
int element = items[top];
top--;
return element;
}
}
public virtual bool Empty
{
get { return (top == -1) ? true : false ; }
}
}
/* prints element and NGE pair for
all elements of arr[] of size n */
public static void printNGE( int [] arr, int n)
{
int i = 0;
stack s = new stack();
s.top = -1;
int element, next;
/* push the first element to stack */
s.push(arr[0]);
// iterate for rest of the elements
for (i = 1; i < n; i++) {
next = arr[i];
if (s.Empty == false ) {
// if stack is not empty, then
// pop an element from stack
element = s.pop();
/* If the popped element is smaller than
next, then a) print the pair b) keep
popping while elements are smaller and
stack is not empty */
while (element < next) {
Console.WriteLine(element + " --> "
+ next);
if (s.Empty == true ) {
break ;
}
element = s.pop();
}
/* If element is greater than next, then
push the element back */
if (element > next) {
s.push(element);
}
}
/* push next to stack so that we can find next
greater for it */
s.push(next);
}
/* After iterating over the loop, the remaining
elements in stack do not have the next greater
element, so print -1 for them */
while (s.Empty == false ) {
element = s.pop();
next = -1;
Console.WriteLine(element + " -- " + next);
}
}
// Driver Code
public static void Main( string [] args)
{
int [] arr = new int [] { 11, 13, 21, 3 };
int n = arr.Length;
printNGE(arr, n);
}
} // This code is contributed by Shrikant13 |
<script> // A Stack based Javascript program to find next // greater element for all array elements. /* prints element and NGE pair for all elements of arr[] of size n */ function printNGE(arr, n)
{ var s = [];
/* push the first element to stack */
s.push(arr[0]);
// iterate for rest of the elements
for ( var i = 1; i < n; i++)
{
if (s.length == 0) {
s.push(arr[i]);
continue ;
}
/* if stack is not empty, then
pop an element from stack.
If the popped element is smaller
than next, then
a) print the pair
b) keep popping while elements are
smaller and stack is not empty */
while (s.length ==0 == false
&& s[s.length-1] < arr[i])
{
document.write( s[s.length-1]
+ " --> " + arr[i]+ "<br>" );
s.pop();
}
/* push next to stack so that we can find
next greater for it */
s.push(arr[i]);
}
/* After iterating over the loop, the remaining
elements in stack do not have the next greater
element, so print -1 for them */
while (s.length !=0) {
document.write( s[s.length-1] + " --> " + -1+ "<br>" );
s.pop();
}
} /* Driver code */ var arr = [11, 13, 21, 3];
var n = arr.length;
printNGE(arr, n); </script> |
11 --> 13 13 --> 21 3 --> -1 21 --> -1
Time Complexity: O(N)
Auxiliary Space: O(N)
Find Next Greater Element using Map:
In this particular approach we are using the map as our main stack
- This is same as above method but the elements are pushed and popped only once into the stack. The array is changed in place. The array elements are pushed into the stack until it finds a greatest element in the right of array. In other words the elements are popped from stack when top of the stack value is smaller in the current array element.
- Once all the elements are processed in the array but stack is not empty. The left out elements in the stack doesn’t encounter any greatest element . So pop the element from stack and change it’s index value as -1 in the array.
// C++ code to implement the approach #include <bits/stdc++.h> using namespace std;
void nextLargerElement( int arr[], int n)
{ vector<unordered_map<string, int > > s;
// iterating over the array
for ( int i = 0; i < n; i++) {
while (s.size() > 0
&& s[s.size() - 1][ "value" ] < arr[i]) {
// updating the array as per the stack top
unordered_map<string, int > d = s[s.size() - 1];
s.pop_back();
arr[d[ "ind" ]] = arr[i];
}
// pushing values to stack
unordered_map<string, int > e;
e[ "value" ] = arr[i];
e[ "ind" ] = i;
s.push_back(e);
}
// updating the array as per the stack top
while (s.size() > 0) {
unordered_map<string, int > d = s[s.size() - 1];
s.pop_back();
arr[d[ "ind" ]] = -1;
}
} // Driver Code int main()
{ int arr[] = { 6, 8, 0, 1, 3 };
int n = 5;
// Function call
nextLargerElement(arr, n);
for ( int i = 0; i < n; i++)
cout << arr[i] << " " ;
} // This code is contributed by phasing17 |
// Java code to implement the approach import java.util.*;
class GFG
{ static void nextLargerElement( int [] arr, int n)
{
ArrayList<HashMap<String, Integer> > s = new ArrayList<HashMap<String, Integer> >();
// iterating over the array
for ( int i = 0 ; i < n; i++) {
while (s.size() > 0
&& s.get(s.size() - 1 ).get( "value" ) < arr[i]) {
// updating the array as per the stack top
HashMap<String, Integer> d = s.get(s.size() - 1 );
s.remove(s.size() - 1 );
arr[d.get( "ind" )] = arr[i];
}
// pushing values to stack
HashMap<String, Integer> e = new HashMap<String, Integer>();
e.put( "value" , arr[i]);
e.put( "ind" , i);
s.add(e);
}
// updating the array as per the stack top
while (s.size() > 0 ) {
HashMap<String, Integer> d = s.get(s.size() - 1 );
s.remove(s.size() - 1 );
arr[d.get( "ind" )] = - 1 ;
}
}
// Driver Code
public static void main(String[] args)
{
int [] arr = { 6 , 8 , 0 , 1 , 3 };
int n = 5 ;
// Function call
nextLargerElement(arr, n);
for ( int i = 0 ; i < n; i++)
System.out.print(arr[i] + " " );
}
} // This code is contributed by phasing17 |
# Python3 code class Solution:
def nextLargerElement( self , arr, n):
# code here
s = []
for i in range ( len (arr)):
while s and s[ - 1 ].get( "value" ) < arr[i]:
d = s.pop()
arr[d.get( "ind" )] = arr[i]
s.append({ "value" : arr[i], "ind" : i})
while s:
d = s.pop()
arr[d.get( "ind" )] = - 1
return arr
if __name__ = = "__main__" :
print (Solution().nextLargerElement([ 6 , 8 , 0 , 1 , 3 ], 5 ))
|
// C# code to implement the approach using System;
using System.Collections.Generic;
class GFG
{ static void nextLargerElement( int [] arr, int n)
{
List<Dictionary< string , int > > s = new List<Dictionary< string , int > >();
// iterating over the array
for ( int i = 0; i < n; i++) {
while (s.Count > 0
&& s[s.Count - 1][ "value" ] < arr[i]) {
// updating the array as per the stack top
Dictionary< string , int > d = s[s.Count - 1];
s.RemoveAt(s.Count - 1);
arr[d[ "ind" ]] = arr[i];
}
// pushing values to stack
Dictionary< string , int > e = new Dictionary< string , int >();
e[ "value" ] = arr[i];
e[ "ind" ] = i;
s.Add(e);
}
// updating the array as per the stack top
while (s.Count > 0) {
Dictionary< string , int > d = s[s.Count - 1];
s.RemoveAt(s.Count - 1);
arr[d[ "ind" ]] = -1;
}
}
// Driver Code
public static void Main( string [] args)
{
int [] arr = { 6, 8, 0, 1, 3 };
int n = 5;
// Function call
nextLargerElement(arr, n);
for ( int i = 0; i < n; i++)
Console.Write(arr[i] + " " );
}
} // This code is contributed by phasing17 |
// JS code to implement the approach function nextLargerElement(arr, n)
{ var s = [];
// iterating over the array
for ( var i = 0; i < arr.length; i++)
{
while (s.length > 0 && s[s.length - 1][ "value" ] < arr[i])
{
// updating the array as per the stack top
var d = s.pop();
arr[d[ "ind" ]] = arr[i];
}
// pushing values to stack
s.push({ "value" : arr[i], "ind" : i});
}
// updating the array as per the stack top
while (s.length > 0)
{
d = s.pop();
arr[d[ "ind" ]] = -1;
}
return arr;
} // Driver Code var arr = [6, 8, 0, 1, 3];
var n = 5;
// Function call console.log(nextLargerElement(arr, n)); // This code is contributed by phasing17 |
8 -1 1 3 -1
Time Complexity: O(N)
Auxiliary Space: O(N)