The correct, optimal and working solution for programming question swap-nodes-algo on hackerrank

/* * Author: Arpit Bhayani * https://arpitbhayani.me */ #include <cmath> #include <cstdio> #include <cstdlib> #include <climits> #include <deque> #include <iostream> #include <list> #include <limits> #include <map> #include <queue> #include <set> #include <stack> #include <vector> #define ll long long #define MIN(a, b) a < b ? a : b #define MAX(a, b) a > b ? a : b using namespace std; int readline(char *str) { int i = 0; char ch; while((ch = getchar()) != '\n') { str[i++] = ch; } str[i] = '\0'; return i; } struct node { int data; struct node * left; struct node * right; }; struct node * new_node(int v) { struct node * t = (struct node *) calloc(1, sizeof(struct node)); t->data = v; return t; } int larr[1025]; int rarr[1025]; void swap_nodes(int root, int k) { int cur_level = 0; queue<int> q; q.push(root); while(!q.empty()) { cur_level++; int count = q.size(); while(count--) { int p = q.front(); q.pop(); if(cur_level % k == 0) { int t = larr[p]; larr[p] = rarr[p]; rarr[p] = t; } if(larr[p] != -1) { q.push(larr[p]); } if(rarr[p] != -1) { q.push(rarr[p]); } } } } void inorder(int root) { if(root == -1) { return; } inorder(larr[root]); printf("%d ", root); inorder(rarr[root]); } int main(int argc, char *argv[]) { int n; scanf("%d", &n); for(int i = 1 ; i <= n ; i++) { int a, b; scanf("%d%d", &a, &b); larr[i] = a; rarr[i] = b; } int t, k; scanf("%d", &t); while(t--) { scanf("%d", &k); swap_nodes(1, k); inorder(1); printf("\n"); } return 0; }