/// <summary>
/// 目标是把周围的人都拽到自己的阵营里面
/// </summary>
private void Dfs(DisJointSet djs, int[][] grid, int row, int col, bool[,] visited)
{
if (visited[row, col])
{
return;
}
visited[row, col] = true;
int rows = grid.Length;
int cols = grid[0].Length;
var upDown = new int[] { -1, 1, 0, 0 };
var leftRight = new int[] { 0, 0, -1, 1 };
for (int i = 0; i < 4; i++)
{
var newRow = row + upDown[i];
var newCol = col + leftRight[i];
if (newRow >= 0 && newRow < rows && newCol >= 0 && newCol < cols && grid[newRow][newCol] == 1)
{
Union(djs, GetIndex(row, col, cols), GetIndex(newRow, newCol, cols), rows * cols);
Dfs(djs, grid, newRow, newCol, visited);
}
}
}
public string SmallestStringWithSwaps(string s, IList <IList <int> > pairs)
{
/*
* 题目概述：交换字符串中同组索引的元素,使得字符串的字母序最小
*
* 思路：
* 1.使用并查集来将给定的索引对拼接成一个大的集体
* 2.找到所有的集体
* 3.将集体所代表的元素排序后写回到原来的字符串中
*
* 关键点：
* 1.直接做字符串排序的话,时间复杂度较高,会超时,因为字符仅有小写字母,因此我自己写了"桶排序"来加速,效果还不错
*
* 时间复杂度：O(n)
* 空间复杂度：O(n)
*/
var DJS = new DisJointSet(s.Length);
foreach (var pairItem in pairs)
{
DJS.Union(pairItem[0], pairItem[1]);
}
var groupDic = new Dictionary <int, IList <int> >();
for (int i = 0; i < s.Length; i++)
{
var groupIndex = DJS.Find(i);
if (!groupDic.ContainsKey(groupIndex))
{
groupDic[groupIndex] = new List <int>();
}
groupDic[groupIndex].Add(i);
}
var forReturnCharArray = s.ToCharArray();
foreach (var groupItem in groupDic)
{
SortedAndInsert(forReturnCharArray, groupItem.Value);
}
return(new string(forReturnCharArray));
}
private void Union(DisJointSet djs, int i, int j, int special)
{
var iParent = djs.Find(i);
var jParent = djs.Find(j);
if (iParent == special)
{
djs.UnionToFrom(i, j);
}
else if (jParent == special)
{
djs.UnionToFrom(j, i);
}
else
{
djs.Union(i, j);
}
}
public int[] HitBricks(int[][] grid, int[][] hits)
{
/*
* 题目概述：打砖块儿
*
* 思路：
* 1.实现并查集,除了Union 和 Find 功能外,还需要一个获取团队人数的功能
* 2.拷贝一份儿砖块儿,把将要打掉的砖块儿全部打掉
* 3.然后逆序把砖块儿加上来,加上来的过程中,特定团队增加的人数,就是要求的解
*
* 关键点：
*
* 时间复杂度：
* 空间复杂度：
*/
int rows = grid.Length;
int cols = grid[0].Length;
var copyGrid = new int[grid.Length][];
for (int r = 0; r < grid.Length; r++)
{
copyGrid[r] = new int[grid[r].Length];
for (int c = 0; c < grid[r].Length; c++)
{
copyGrid[r][c] = grid[r][c];
}
}
for (int i = 0; i < hits.Length; i++)
{
var r = hits[i][0];
var c = hits[i][1];
copyGrid[r][c] = 0;
}
var djs = new DisJointSet(rows * cols + 1);
var visited = new bool[rows, cols];
var specialNum = rows * cols;
for (int r = 0; r < copyGrid.Length; r++)
{
for (int c = 0; c < copyGrid[r].Length; c++)
{
if (copyGrid[r][c] == 0)
{
continue;
}
if (r == 0)
{
Union(djs, specialNum, GetIndex(r, c, cols), specialNum);
}
Dfs(djs, copyGrid, r, c, visited);
}
}
var forReturn = new int[hits.Length];
var initTotal = djs.GetCount(specialNum);
for (int i = hits.Length - 1; i >= 0; i--)
{
var r = hits[i][0];
var c = hits[i][1];
var tempValue = 0;
if (grid[r][c] != 0)
{
copyGrid[r][c] = 1;
if (r == 0)
{
Union(djs, specialNum, GetIndex(r, c, cols), specialNum);
}
var upDownArray = new int[] { -1, 1, 0, 0 };
var leftRightArray = new int[] { 0, 0, -1, 1 };
for (int j = 0; j < 4; j++)
{
var newR = r + upDownArray[j];
var newC = c + leftRightArray[j];
if (newR < 0 || newR >= rows || newC < 0 || newC >= cols || copyGrid[newR][newC] != 1)
{
continue;
}
Union(djs, GetIndex(r, c, cols), GetIndex(newR, newC, cols), specialNum);
}
var temp = djs.GetCount(specialNum);
tempValue = temp - initTotal - 1;
if (tempValue < 0)
{
tempValue = 0;
}
initTotal = temp;
}
forReturn[i] = tempValue;
}
return(forReturn);
}