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128.java
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128.java
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//https://leetcode.com/problems/longest-consecutive-sequence/
public class UF{
public int[] parent;
public int[] height;
public int result=0;
public UF(int n){
parent=new int[n];
height = new int[n];
for(int i=0;i<n;i++){
parent[i]=i;
}
}
public int findRoot(int i){
while(parent[i]!=i) i=parent[i];
return i;
}
public boolean find(int i, int j){
return findRoot(i)==findRoot(j);
}
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]++;
}
}
public int maxUnion(){
int[] count=new int[parent.length];
for(int i=0;i<parent.length;i++){
int root = findRoot(i);
count[root]++;
result=Math.max(result, count[root]);
}
return result;
}
}
public int longestConsecutive(int[] nums) {
if(nums==null || nums.length==0) return 0;
UF unionFind =new UF(nums.length);
HashMap<Integer, Integer> map=new HashMap<>();
for(int i=0;i<nums.length;i++){
if(map.containsKey(nums[i])) continue;
map.put(nums[i], i);
if(map.containsKey(nums[i]+1)){
unionFind.union(i, map.get(nums[i]+1));
}
if(map.containsKey(nums[i]-1)){
unionFind.union(i, map.get(nums[i]-1));
}
}
return unionFind.maxUnion();
}