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文章目录
前言
并查集（Union-Find）算法是一个专门针对「动态连通性」的算法，我之前写过两次，因为这个算法的考察频率高，而且它也是最小生成树算法的前置知识，所以我整合了本文，争取一篇文章把这个算法讲明白
一、力扣990. 等式方程的可满足性
class Solution {
public boolean equationsPossible(String[] equations) {
if(equations == null || equations.length == 0){
return true;
}
int n = equations.length;
Uf uf = new Uf(27);
for(int i = 0; i < n; i ++){
char c1 = equations[i].charAt(1);
if(c1 == '='){
int x = equations[i].charAt(0) - 'a';
int y = equations[i].charAt(3) - 'a';
uf.union(x,y);
}
}
for(int i = 0; i < n; i ++){
if(equations[i].charAt(1) == '!'){
int x = equations[i].charAt(0) - 'a';
int y = equations[i].charAt(3) - 'a';
if(uf.getConnection(x, y)){
return false;
}
}
}
return true;
}
class Uf{
private int count;
private int[] parent;
public Uf(int n){
this.count = n;
this.parent = new int[n];
for(int i = 0; i < n; i ++){
parent[i] = i;
}
}
public int getCount(){
return count;
}
public int find(int x){
if(parent[x] != x){
parent[x] = find(parent[x]);
}
return parent[x];
}
public boolean getConnection(int x, int y){
int rootx = find(x);
int rooty = find(y);
return rootx == rooty;
}
public void union(int x, int y){
int rootx = find(x);
int rooty = find(y);
if(rootx == rooty){
return;
}
this.parent[rootx] = rooty;
count --;
}
}
}
