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package class13;
// 本题测试链接 : https://leetcode.com/problems/bricks-falling-when-hit/
public class Code04_BricksFallingWhenHit {
public static int[] hitBricks(int[][] grid, int[][] hits) {
for (int i = 0; i < hits.length; i++) {
if (grid[hits[i][0]][hits[i][1]] == 1) {
grid[hits[i][0]][hits[i][1]] = 2;
}
}
UnionFind unionFind = new UnionFind(grid);
int[] ans = new int[hits.length];
for (int i = hits.length - 1; i >= 0; i--) {
if (grid[hits[i][0]][hits[i][1]] == 2) {
ans[i] = unionFind.finger(hits[i][0], hits[i][1]);
}
}
return ans;
}
// 并查集
public static class UnionFind {
private int N;
private int M;
// 有多少块砖,连到了天花板上
private int cellingAll;
// 原始矩阵因为炮弹的影响1 -> 2
private int[][] grid;
// cellingSet[i] = true; i 是头节点,所在的集合是天花板集合
private boolean[] cellingSet;
private int[] fatherMap;
private int[] sizeMap;
private int[] stack;
public UnionFind(int[][] matrix) {
initSpace(matrix);
initConnect();
}
private void initSpace(int[][] matrix) {
grid = matrix;
N = grid.length;
M = grid[0].length;
int all = N * M;
cellingAll = 0;
cellingSet = new boolean[all];
fatherMap = new int[all];
sizeMap = new int[all];
stack = new int[all];
for (int row = 0; row < N; row++) {
for (int col = 0; col < M; col++) {
if (grid[row][col] == 1) {
int index = row * M + col;
fatherMap[index] = index;
sizeMap[index] = 1;
if (row == 0) {
cellingSet[index] = true;
cellingAll++;
}
}
}
}
}
private void initConnect() {
for (int row = 0; row < N; row++) {
for (int col = 0; col < M; col++) {
union(row, col, row - 1, col);
union(row, col, row + 1, col);
union(row, col, row, col - 1);
union(row, col, row, col + 1);
}
}
}
private int find(int row, int col) {
int stackSize = 0;
int index = row * M + col;
while (index != fatherMap[index]) {
stack[stackSize++] = index;
index = fatherMap[index];
}
while (stackSize != 0) {
fatherMap[stack[--stackSize]] = index;
}
return index;
}
private void union(int r1, int c1, int r2, int c2) {
if (valid(r1, c1) && valid(r2, c2)) {
int father1 = find(r1, c1);
int father2 = find(r2, c2);
if (father1 != father2) {
int size1 = sizeMap[father1];
int size2 = sizeMap[father2];
boolean status1 = cellingSet[father1];
boolean status2 = cellingSet[father2];
if (size1 <= size2) {
fatherMap[father1] = father2;
sizeMap[father2] = size1 + size2;
if (status1 ^ status2) {
cellingSet[father2] = true;
cellingAll += status1 ? size2 : size1;
}
} else {
fatherMap[father2] = father1;
sizeMap[father1] = size1 + size2;
if (status1 ^ status2) {
cellingSet[father1] = true;
cellingAll += status1 ? size2 : size1;
}
}
}
}
}
private boolean valid(int row, int col) {
return row >= 0 && row < N && col >= 0 && col < M && grid[row][col] == 1;
}
public int cellingNum() {
return cellingAll;
}
public int finger(int row, int col) {
grid[row][col] = 1;
int cur = row * M + col;
if (row == 0) {
cellingSet[cur] = true;
cellingAll++;
}
fatherMap[cur] = cur;
sizeMap[cur] = 1;
int pre = cellingAll;
union(row, col, row - 1, col);
union(row, col, row + 1, col);
union(row, col, row, col - 1);
union(row, col, row, col + 1);
int now = cellingAll;
if (row == 0) {
return now - pre;
} else {
return now == pre ? 0 : now - pre - 1;
}
}
}
}