public int[] FindRedundantConnection(int[][] edges)
{
if (edges.Length == 1)
{
return(Array.Empty <int>());
}
Span <int> id = stackalloc int[edges.Length];
Span <int> rank = stackalloc int[edges.Length];
var uf = new SpanUF(id, rank);
foreach (var edge in edges)
{
uf.Union(edge[0] - 1, edge[1] - 1);
}
return(uf.GetRedundantConnection());
}
public int NumIslands(char[][] grid)
{
if (grid is null || grid.Length == 0)
{
return(0);
}
var rowCount = grid.Length;
var colCount = grid[0].Length;
var n = rowCount * colCount;
// initialize UF
Span <int> id = stackalloc int[n];
Span <int> sz = stackalloc int[n];
var count = 0;
for (var i = 0; i < rowCount; i++)
{
for (var j = 0; j < colCount; j++)
{
if (grid[i][j] == '1')
{
var idx = i * colCount + j;
id[idx] = idx;
sz[idx] = 1;
count += 1;
}
}
}
var uf = new SpanUF(id, sz, count);
for (var i = 0; i < rowCount; i++)
{
for (var j = 0; j < colCount; j++)
{
if (grid[i][j] == '1')
{
// grid[i][j] = '0'; avoid duplicate Union action
var p = i * colCount + j;
uf.Union(p, grid, rowCount, colCount);
}
}
}
return(uf.Count);
}