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Linked List Random Node in C++
Suppose we have a singly linked list, we have to find a random node's value from the linked list. Here each node must have the same probability of being chosen. So for example, if the list is [1,2,3], then it can return random node in range 1, 2, and 3.
To solve this, we will follow these steps −
In the getRandom() method, do the following −
ret := -1, len := 1, v := x
while v is not null
if rand() is divisible by len, then ret := val of v
increase len by 1
v := next of v
return ret
Example(C++)
Let us see the following implementation to get a better understanding −
#include <bits/stdc++.h>
using namespace std;
class ListNode{
public:
int val;
ListNode *next;
ListNode(int data){
val = data;
next = NULL;
}
};
ListNode *make_list(vector<int> v){
ListNode *head = new ListNode(v[0]);
for(int i = 1; i<v.size(); i++){
ListNode *ptr = head;
while(ptr->next != NULL){
ptr = ptr->next;
}
ptr->next = new ListNode(v[i]);
}
return head;
}
class Solution {
public:
ListNode* x;
Solution(ListNode* head) {
srand(time(NULL));
x = head;
}
int getRandom() {
int ret = -1;
int len = 1;
ListNode* v = x;
while(v){
if(rand() % len == 0){
ret = v->val;
}
len++;
v = v->next;
}
return ret;
}
};
main(){
vector<int> v = {1,7,4,9,2,5};
ListNode *head = make_list(v);
Solution ob(head);
cout << (ob.getRandom());
}Input
Initialize list with [1,7,4,9,2,5] Call getRandom() to get random nodes
Output
4 9 1
Updated on: 02-May-2020
255 Views
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