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groups-of-strings.cpp
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groups-of-strings.cpp
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// Time: O(26 * n)
// Space: O(26 * n)
// bitmasks, union find
class Solution {
public:
vector<int> groupStrings(vector<string>& words) {
UnionFind uf(size(words));
unordered_map<int, int> lookup;
for (int i = 0; i < size(words); ++i) {
const int mask = accumulate(cbegin(words[i]), cend(words[i]), 0, [](int total, int x) {
return total | (1 << (x - 'a'));
});
if (!lookup.count(mask)) {
lookup[mask] = i;
}
uf.union_set(i, lookup[mask]);
for (int bit = 1; bit <= mask; bit <<= 1) {
if (mask & bit) {
if (!lookup.count(mask ^ bit)) {
lookup[mask ^ bit] = i;
}
uf.union_set(i, lookup[mask ^ bit]);
}
}
}
return {uf.total(), uf.max_size()};
}
private:
class UnionFind {
public:
UnionFind(int n)
: set_(n)
, rank_(n)
, size_(n, 1)
, total_(n) {
iota(set_.begin(), set_.end(), 0);
}
int find_set(int x) {
if (set_[x] != x) {
set_[x] = find_set(set_[x]); // Path compression.
}
return set_[x];
}
bool union_set(int x, int y) {
x = find_set(x), y = find_set(y);
if (x == y) {
return false;
}
if (rank_[x] > rank_[y]) {
swap(x, y);
}
set_[x] = y; // Union by rank.
if (rank_[x] == rank_[y]) {
++rank_[y];
}
size_[y] += size_[x];
--total_;
return true;
}
int max_size() {
return *max_element(cbegin(size_), cend(size_));
}
int total() {
return total_;
}
private:
vector<int> set_;
vector<int> rank_;
vector<int> size_;
int total_;
};
};