8. Next greater node in linked list

Linked List/C++/8_Next_greater_node_in_linked_list.cpp

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+/*
+
+Problem: Next greater node in linked list
+
+Description:
+A linked list is given with head as the first node. Let's number the nodes in the list: node_1, node_2, node_3, ... etc.
+Each node may have a next larger value: for node_i, next_larger(node_i) is the node_j.val such that j > i, node_j.val > node_i.val, and j is the smallest possible choice.  If such a j does not exist, the next larger value is 0.
+
+This solution returns an array of integers answer, where answer[i] = next_larger(node_{i+1}).  (Ex: answer[0] = next_larger(node_1))
+
+Note:
+1 <= node.val <= 10^9 for each node in the linked list.
+The given list has length in the range [0, 10000].
+
+*/
+
+#include<iostream>
+#include<vector>
+#include<bits/stdc++.h>
+
+using namespace std;
+
+//Definition for Singly-linked list
+struct ListNode {
+	int val;
+	ListNode *next;
+	ListNode() : val(0), next(nullptr) {}
+	ListNode(int x) : val(x), next(nullptr) {}
+	ListNode(int x, ListNode *next) : val(x), next(next) {}
+};
+
+class Solution {
+public:
+    vector<int> nextLargerNodes(ListNode* head) {
+        vector<int> ans; // Answer array
+
+        // returns an empty set if input is null (0 nodes) i.e., head is null
+        if(head==NULL){
+        	return ans;
+		}
+
+        while(head->next!=NULL) {
+            ListNode* temp=head; //temporary node pointing to node_i 
+            head=head->next;
+
+            // initially lets assume there is no node with greater value than the initial node value. x represents the the next larger node value. 
+            int x=0;
+            while(head!=NULL) {
+            	//Checks if greater value exists:
+                if(head->val>temp->val) {
+                    x=head->val;
+                    break; 
+                }
+                head=head->next;
+            }
+            ans.push_back(x); //Adds x to the answer array
+            head=temp;
+            head=head->next;
+        }
+        ans.push_back(0); // Last node has no next node (as j does not esixt). Hence, has no next greater node. 
+
+        return ans;
+    }
+};
+
+int main() {
+
+	int t;
+	cout<<"Enter the number of test cases: ";
+	cin>>t;
+
+	for(int i=1;i<=t;i++) {
+
+		Solution* s = new Solution;
+
+		cout<<"Enter the number of nodes: ";
+		int n; // Number of nodes
+		cin>>n;
+
+		if(n>=1) {
+			int head;
+			cout<<"Enter node values: \n";
+			cin>>head; // Head node	value
+			ListNode* h;
+			ListNode* t1 = new ListNode(head);  // Node pointing to the head node
+			h=t1;
+			for(int j=1;j<n;j++) {
+				int v;
+				cin>>v;
+				h->next = new ListNode(v);
+				h=h->next;	
+			}
+			h=t1; // Node h points back to the head of the linked-list
+
+			vector<int> answer(n); //Creating an array with size of number of nodes.
+			answer = s->nextLargerNodes(h); // Answer array consists of next larger node value for every node in order.
+
+			cout<<"Answer: [";
+			for(int k=0;k<answer.size();k++) {
+				cout<<answer[k]<<" ";
+			}
+			cout<<"]"<<endl;
+		}
+
+		// If the head node is null
+		else {
+			cout<<"Answer: []\n";
+		}	
+	}
+
+	return 0;
+
+}
+
+/*
+// Accepted
+
+SAMPLE INPUT:
+5                                     -> Number of testcases
+3 2 1 5                               -> First testcase. First input represents the number of nodes, rest are the node values. 
+5 2 7 4 3 5                           -> Second testcase
+8 1 7 5 1 9 2 5 1                     -> Third testcase
+1 5                                   -> Testcase with a single node
+0                                     -> Testcase with zero nodes     
+
+SAMPLE OUTPUT: (excusive of interactive instructions)
+[5 5 0]                                 
+[7 0 5 5 0]
+[7 9 9 9 0 5 0 0]
+[0]
+[]
+
+Explanation:
+First input of every testcase represents number of nodes.
+
+Testcase 1:
+Inputs following the first input i.e., 3(number of nodes) represent the serialization of a linked list with a head node value of 2, second node value of 1, and third node value of 5.
+The next node value greater than 2 is 5. The next node value greater than 1 is 5. last node value 5 has no next node.
+
+Testcase 2:
+Head node val = 2. Next greater node val is 7. 
+Second node val = 7. Next greater node does not exist. Hence outputs 0.
+Third node val = 4. Next greater node val is 5.
+Fourth node val = 3. Next greater node val is 5. 
+Fifth node val = 5. Next node does not exist. Hnece outputs 0.
+
+(Same for testcase 3)
+
+Testcase 4: 
+Head node = 5. Next node does not exist. Hence outputs 0.
+
+Testcase 5:
+Head node does not exist. Hence outputs an empty array.
+
+
+Time complexity: O(n^2)  
+n= number of nodes.
+
+*/