I'm working on a coding question and I'm given an array for example something like this: [1, 7, 3, 21, 13, 19]
I'm suppose to pair up items in the array. Then after that I'm suppose to apply this simple rule.
Say I choose a pair x and y:
Rule:
if x > y : y = 2*y and x = x - y
if y > x : x = 2*x and y = y - x
if x == y : break # x and y is a pair that does not cause an infinite loop
Example:
Say x = 7 and y = 3
1st round : x = 7 and y = 3
2nd round : x = 4 and y = 6
3rd round : x = 8 and y = 2
4th round : x = 6 and y = 4
at this point you know that this pair will loop forever
If for example x = 1 and y = 3
1st round : x = 1 and y = 3
2nd round : x = 2 and y = 2
At this point you know that this pair doesn't loop
So in order to solve this problem. I saw it as some kind of TSP but instead of minimizing path, I'm maximizing path.
So first step I did is create a graph of nodes and label whether a pair is a loop or not
In this array the graph generated (adjacency matrix) is this:
0 0 0 1 1 1
0 0 1 0 1 1
0 1 0 0 0 1
1 0 0 0 1 1
1 1 0 1 0 0
1 1 1 1 0 0
the index in the graph represent index in the array. For example let's say that i is row and j is column. If you look at i=0, j=2 that represents array[i] = x, array[j] = y which is array[0] = x = 1, array[2] = y = 3. From the above example we know that that is not a loop. Therefore there is a 0 weight on that index.
Then I do a nearest neighbor TSP algorithm (modified to be max route) in order to get the max pair that maximized the amount of loop pairs. This method passes the coding test cases except for one. I can't identify an array of integers that would fail my code. And the test cases on the coding challenge does not give me any info on what test it is failing on.
Here is my code:
import java.util.HashMap;
public class DistractTheGuards {
private static boolean IsPairLoop(int first, int second)
{
long result = first + second;
boolean success = true;
while ((result & 1) == 0)
{
if (first == second)
{
success = false;
break;
}
else if (first > second)
{
first = (first - second) / 2;
}
else
{
second = (second - first) / 2;
}
result = first + second;
}
return success;
}
public static void GenWeights(int[][] graph, int[] banana_list)
{
for (int i = 0; i < graph.length; ++i)
{
for (int j = 0; j < graph.length; ++j)
{
if (IsPairLoop(banana_list[i], banana_list[j]))
{
graph[i][j] = 1;
}
else
{
graph[i][j] = 0;
}
}
}
}
private static boolean AreAllNodesVisited(boolean[] visited)
{
boolean all_visited = true;
for (int i = 0; i < visited.length; ++i)
{
all_visited &= visited[i];
if (!all_visited)
break;
}
return all_visited;
}
private static int FindMaxTourKey(HashMap<Integer, int[]> tours)
{
int cur_max_r = -1;
for (Integer rank : tours.keySet())
{
if (cur_max_r < rank)
cur_max_r = rank;
}
return cur_max_r;
}
private static int GetN(int[][] graph, int[] max_tour, int n)
{
for (int i = 0; i < max_tour.length; i += 2)
{
if (i + 1 >= max_tour.length)
break;
if (graph[max_tour[i]][max_tour[i+1]] == 0)
{
n -= 2;
}
}
return n;
}
public static int answer(int[] banana_list)
{
int n = banana_list.length;
if (n < 1)
return 0;
if (n == 1)
return 1;
int[][] graph = new int[n][n];
GenWeights(graph, banana_list);
HashMap<Integer, int[]> tours = new HashMap<>();
for (int i = 0; i < n; ++i)
{
int[] cur_tour = new int[n];
boolean[] visited = new boolean[n];
int start_node = i;
int cur_tour_i = 0;
while (!AreAllNodesVisited(visited))
{
int s_n = start_node;
visited[start_node] = true;
cur_tour[cur_tour_i++] = start_node;
int cur_max = 0;
for (int j = 0; j < n; ++j)
{
if (!visited[j])
{
if (cur_max < graph[start_node][j])
{
cur_max = graph[start_node][j];
start_node = j;
break;
}
}
}
if (s_n == start_node)
{
for (int x = n - 1; x >= 0; --x)
{
if (!visited[x])
{
start_node = x;
break;
}
}
}
}
int cur_tour_r = 0;
for (int x = 0; x < n; x += 2)
{
if (x + 1 >= n)
break;
cur_tour_r += graph[cur_tour[x]][cur_tour[x+1]];
}
tours.put(cur_tour_r, cur_tour.clone());
if (cur_tour_r == n - 1)
break;
}
int cur_max_r = FindMaxTourKey(tours);
if (tours.size() == 0)
return 0;
int[] max_tour = tours.get(cur_max_r);
return GetN(graph, max_tour, n);
}
}
I just need help identifying an edge case that would fail my method. Can anyone help me or give me an array that would certainly fail my method? I can take it from there. Thanks
Update
Constraints
1 <= integers <= 2^30
1 <= len(array) <= 100
