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LeetCode-547-Friend-Circles.java
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LeetCode-547-Friend-Circles.java
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// 1. UnionFind
/*
Runtime: 1 ms, faster than 100.00% of Java online submissions for Friend Circles.
Memory Usage: 45.2 MB, less than 40.00% of Java online submissions for Friend Circles.
*/
class Solution {
private class UnionFind {
int[] id, size;
int count;
public UnionFind(int len) {
this.id = new int[len];
this.size = new int[len];
for (int i = 0; i < len; i++) {
id[i] = i;
size[i] = i;
}
this.count = len;
}
public int size() {
return count;
}
private int root(int i) {
while (i != id[i]) {
id[i] = id[id[i]];
i = id[i];
}
return i;
}
public boolean find(int p, int q) {
return root(p) == root(q);
}
public void union(int p, int q) {
int pi = root(p), qi = root(q);
if (pi == qi) return;
if (size[pi] < size[qi]) {
id[pi] = qi;
size[qi] += size[pi];
} else {
id[qi] = pi;
size[pi] += size[qi];
}
count--;
}
}
public int findCircleNum(int[][] M) {
UnionFind uf = new UnionFind(M.length);
for (int i = 0; i < M.length; i++) {
for (int j = i + 1; j < M.length; j++) {
if (M[i][j] == 1) {
uf.union(i, j);
}
}
}
return uf.size();
}
}