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Create 305.cpp

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Kirigaya Kazuto 2022-09-14 21:47:38 +08:00 committed by GitHub
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commit ba609b3657
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class DisjointSet
{
public:
int* parent;
int countRoot;
DisjointSet(int size) {
parent = new int[size + 1];
memset(parent, 0, sizeof(int) * (size + 1));
countRoot = 0;
}
int find(int id) {
if (parent[id] && 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 {
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:
vector<int> numIslands2(int m, int n, vector<vector<int>>& positions) {
int sz = m * n;
DisjointSet dset(sz);
vector<int> results;
for (auto& pr : positions) {
int line = pr[0];
int col = pr[1];
int id = line * n + col + 1;
if (dset.parent[id]) {
results.push_back(dset.countRoot);
continue;
}
dset.setParent(id, id);
if (line > 0) {
int upid = (line - 1) * n + col + 1;
if (dset.parent[upid]) dset.setParent(upid, id);
}
if (line < m - 1) {
int downid = (line + 1) * n + col + 1;
if(dset.parent[downid]) dset.setParent(downid, id);
}
if (col > 0) {
int leftid = line * n + col;
if (dset.parent[leftid]) dset.setParent(leftid, id);
}
if (col < n - 1) {
int rightid = line * n + col + 2;
if (dset.parent[rightid]) dset.setParent(rightid, id);
}
results.push_back(dset.countRoot);
}
return results;
}
};