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305.java
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305.java
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//https://leetcode.com/problems/number-of-islands-ii/
public class UF{
public int[] parent;
public int[] height;
public int count;
public UF(int m, int n){
count=0;
parent=new int[m*n];
height=new int[m*n];
for(int i=0;i<m*n;i++) parent[i]=i;
}
public boolean find(int i,int j){
return findRoot(i)==findRoot(j);
}
public int findRoot(int i){
while(parent[i]!=i) i=parent[i];
return i;
}
public void union(int i, int j){
i=findRoot(i);
j=findRoot(j);
if(i==j) return;
if(height[i]>height[j]){
parent[j]=i;
}
else if(height[i]<height[j]){
parent[i]=j;
}
else{
parent[i]=j;
height[j]++;
}
count--;
}
}
public List<Integer> numIslands2(int m, int n, int[][] positions) {
List<Integer> result=new LinkedList<Integer>();
if(m<0 || n<0) return result;
if(positions==null ) return result;
UF unionFind=new UF(m,n);
int[][] matrix=new int[m][n];
for(int[] e: positions){
int i=e[0];
int j=e[1];
if(matrix[i][j]==1){
result.add(unionFind.count);
continue;
}
matrix[i][j]=1;
unionFind.count++;
int p=i*n+j;
if(i>0 && matrix[i-1][j]==1){
unionFind.union(p, p-n);
}
if(i<m-1 && matrix[i+1][j]==1){
unionFind.union(p, p+n);
}
if(j>0 && matrix[i][j-1]==1){
unionFind.union(p, p-1);
}
if(j<n-1 && matrix[i][j+1]==1){
unionFind.union(p, p+1);
}
result.add(unionFind.count);
}
return result;
}