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Copy pathDSU.java
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70 lines (64 loc) · 1.48 KB
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class DSU {
private int n;
private int[] parentOrSize;
public DSU(int n) {
this.n = n;
this.parentOrSize = new int[n];
Arrays.fill(parentOrSize, -1);
}
int merge(int a, int b) {
if (!(0 <= a && a < n) || !(0 <= b && b < n)) {
// この式が成立しない物は動作しません。
return -1;
}
int x = leader(a);
int y = leader(b);
if (x == y) return x;
if (-parentOrSize[x] < -parentOrSize[y]) {
int tmp = x;
x = y;
y = tmp;
}
parentOrSize[x] += parentOrSize[y];
parentOrSize[y] = x;
return x;
}
boolean same(int a, int b) {
if (!(0 <= a && a < n) || !(0 <= b && b < n)) {
// この式が成立しない物は動作しません。
return false;
}
return leader(a) == leader(b);
}
int leader(int a) {
if (parentOrSize[a] < 0) {
return a;
} else {
parentOrSize[a] = leader(parentOrSize[a]);
return parentOrSize[a];
}
}
int size(int a) {
if (!(0 <= a && a < n)) {
// この式が成立しない物は動作しません。
return -1;
}
return -parentOrSize[leader(a)];
}
ArrayList<ArrayList<Integer>> groups() {
int[] leaderBuf = new int[n];
int[] groupSize = new int[n];
for (int i = 0; i < n; i++) {
leaderBuf[i] = leader(i);
groupSize[leaderBuf[i]]++;
}
ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
for (int i = 0; i < n; i++) {
result.add(new ArrayList<>());
}
for (int i = 0; i < n; i++) {
result.get(leaderBuf[i]).add(i);
}
return result;
}
}