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Kirigaya Kazuto 2022-09-18 09:39:06 +08:00 committed by GitHub
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commit 607bf799c0
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class DisjointSet
{
public:
int* parent;
int countRoot;
DisjointSet(int size) {
parent = new int[size];
memset(parent, 0xFF, sizeof(int) * size);
countRoot = 0;
}
~DisjointSet() {
delete[] parent;
}
int find(int id) {
if (parent[id] != -1 && parent[id] != id) {
parent[id] = find(parent[id]);
}
// printf("parent of %d is %d\n", id, parent[id]);
return parent[id];
}
void setParent(int child, int upper) {
if (upper == child) {
parent[child] = child;
countRoot++;
}
else {
if (parent[child] == -1) {
parent[child] = child;
countRoot++;
}
if (parent[upper] == -1) {
parent[upper] = upper;
countRoot++;
}
int childRoot = find(child);
int upperRoot = find(upper);
if (childRoot != upperRoot) countRoot--;
// printf("set parent of %d to %d\n", childRoot, upperRoot);
parent[childRoot] = upperRoot;
}
}
};
class Solution {
public:
int largestIsland(vector<vector<int>>& grid) {
int n = grid.size();
DisjointSet dset = DisjointSet(n * n);
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (!grid[i][j]) continue;
if (dset.find(i * n + j) == -1) {
dset.setParent(i * n + j, i * n + j);
}
if (i > 0 && grid[i - 1][j]) {
dset.setParent((i - 1) * n + j, i * n + j);
}
if (i < n - 1 && grid[i + 1][j]) {
dset.setParent((i + 1) * n + j, i * n + j);
}
if (j > 0 && grid[i][j - 1]) {
dset.setParent(i * n + j - 1, i * n + j);
}
if (j < n - 1 && grid[i][j + 1]) {
dset.setParent(i * n + j + 1, i * n + j);
}
}
}
unordered_map<int, int> areaMap;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (!grid[i][j]) continue;
int root = dset.find(i * n + j);
auto iter = areaMap.find(root);
if (iter != areaMap.end()) {
iter->second++;
}
else {
areaMap.insert_or_assign(root, 1);
}
}
}
int maxArea = 0;
for (auto iter = areaMap.begin(); iter != areaMap.end(); iter++) {
maxArea = max(maxArea, iter->second);
}
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (grid[i][j]) continue;
unordered_set<int> usedRoot;
int totalArea = 1;
if (i > 0 && grid[i-1][j]) {
int root = dset.find((i - 1) * n + j);
if (usedRoot.find(root) == usedRoot.end()) {
usedRoot.insert(root);
int area = areaMap.find(root)->second;
totalArea += area;
}
}
if (i < n - 1 && grid[i + 1][j]) {
int root = dset.find((i + 1) * n + j);
if (usedRoot.find(root) == usedRoot.end()) {
usedRoot.insert(root);
int area = areaMap.find(root)->second;
totalArea += area;
}
}
if (j > 0 && grid[i][j - 1]) {
int root = dset.find(i * n + j - 1);
if (usedRoot.find(root) == usedRoot.end()) {
usedRoot.insert(root);
int area = areaMap.find(root)->second;
totalArea += area;
}
}
if (j < n - 1 && grid[i][j + 1]) {
int root = dset.find(i * n + j + 1);
if (usedRoot.find(root) == usedRoot.end()) {
usedRoot.insert(root);
int area = areaMap.find(root)->second;
totalArea += area;
}
}
maxArea = max(maxArea, totalArea);
}
}
return maxArea;
}
};