def getEnd(i):
while nodes[i][1] != 0: i = nodes[i][1]-1
return i
n = int(input())
nodes = [list(map(int, input().split())) for _ in range(n)]
starts = [i for i in range(n) if nodes[i][0] == 0]
ends = [getEnd(i) for i in starts]
for i in range(len(starts)-1):
nodes[ends[i]][1] = starts[i+1]+1
nodes[starts[i+1]][0] = ends[i]+1
for row in nodes: print(*row)
62. Unique Paths | 50. Pow(x, n) |
43. Multiply Strings | 34. Find First and Last Position of Element in Sorted Array |
33. Search in Rotated Sorted Array | 17. Letter Combinations of a Phone Number |
5. Longest Palindromic Substring | 3. Longest Substring Without Repeating Characters |
1312. Minimum Insertion Steps to Make a String Palindrome | 1092. Shortest Common Supersequence |
1044. Longest Duplicate Substring | 1032. Stream of Characters |
987. Vertical Order Traversal of a Binary Tree | 952. Largest Component Size by Common Factor |
212. Word Search II | 174. Dungeon Game |
127. Word Ladder | 123. Best Time to Buy and Sell Stock III |
85. Maximal Rectangle | 84. Largest Rectangle in Histogram |
60. Permutation Sequence | 42. Trapping Rain Water |
32. Longest Valid Parentheses | Cutting a material |
Bubble Sort | Number of triangles |
AND path in a binary tree | Factorial equations |
Removal of vertices | Happy segments |