// 695. Max Area of Island
public int MaxAreaOfIsland(int[][] grid)
{
var m = grid.Length;
var n = grid[0].Length;
var totalLength = m * n;
var uf = new UnionFind(totalLength + 1);
var maxArea = 0;
for (int i = 0; i < m; i++)
{
for (int j = 0; j < n; j++)
{
if (grid[i][j] == 0)
{
uf.Union(i * n + j, totalLength);
}
else
{
if (j + 1 < n && grid[i][j + 1] == 1)
{
uf.Union(i * n + j, i * n + j + 1);
}
if (i + 1 < m && grid[i + 1][j] == 1)
{
uf.Union((i + 1) * n + j, i * n + j);
}
maxArea = Math.Max(maxArea, uf.FindSize(i * n + j));
}
}
}
return(maxArea);
}
// 128. Longest Consecutive Sequence
// A small tweak on UnionFind to add the FindSize method for this problem
public int LongestConsecutive(int[] nums)
{
var uf = new UnionFind(nums.Length);
var dict = new Dictionary <int, int>();
var maxLength = 0;
for (int i = 0; i < nums.Length; i++)
{
if (!dict.ContainsKey(nums[i]))
{
dict.Add(nums[i], i);
}
else
{
continue;
}
if (dict.ContainsKey(nums[i] - 1))
{
uf.Union(i, dict[nums[i] - 1]);
}
if (dict.ContainsKey(nums[i] + 1))
{
uf.Union(i, dict[nums[i] + 1]);
}
maxLength = Math.Max(maxLength, uf.FindSize(i));
}
return(maxLength);
}
public int CalculateEnclosedArea(int[][] grid)
{
var m = grid.Length;
var n = grid[0].Length;
var totalCells = m * n;
var uf = new UnionFind(totalCells + 3);
// uf[totalCells] -> 0 cell that is not enclosed,
// uf[totalCells + 1] -> wall cells(value >= 1),
// uf[totalCells + 2] -> enclosed 0 cells
for (int i = 0; i < m; i++)
{
for (int j = 0; j < n; j++)
{
if (grid[i][j] > 0)
{
uf.Union(i * n + j, totalCells + 1);
}
if (grid[i][j] == 0)
{
if (i == 0 || j == 0 || i == m - 1 || j == n - 1)
{
uf.Union(i * n + j, totalCells);
}
if (i + 1 < m && grid[i + 1][j] == 0)
{
uf.Union(i * n + j, (i + 1) * n + j);
}
if (j + 1 < n && grid[i][j + 1] == 0)
{
uf.Union(i * n + j, i * n + j + 1);
}
}
}
}
for (int i = 0; i < m; i++)
{
for (int j = 0; j < n; j++)
{
if (grid[i][j] == 0 && !uf.Connected(i * n + j, totalCells))
{
uf.Union(i * n + j, totalCells + 2);
}
}
}
return(uf.FindSize(totalCells + 2) - 1);
}
