Q39 Satisfiability of Equality Equations - LeetCode 990

class Solution {
    public boolean equationsPossible(String[] equations) {
        /* Q39 graph playlist , DSU concept
        1) union all letters with ==
        
        2) process equations with != , if any 2 variable have same parent return false
        */

        int n = equations.length;
        parent = new int[26];       //total letters 26
        size = new int[26];

        for(int i = 0 ;i < 26 ; i++){
            parent[i] = i;
            size[i] = 1;
        }
        
        //unioning all equations variables with '=='

        for(String eq : equations){
            int a = (eq.charAt(0) - 'a') ;
            int b = (eq.charAt(3) - 'a') ;
            
            char symbol = eq.charAt(1);

            if(symbol == '=')
            union(a,b);
        }


        //processing equations with !=
        for(String eq : equations){
            int a = (eq.charAt(0) - 'a') ;
            int b = (eq.charAt(3) - 'a') ;
            
            char symbol = eq.charAt(1);

            if(symbol == '!'){
                int p1 = findparent(a) , p2 = findparent(b);

                if(p1 == p2)
                return false;
            }
        }

        return true;
        
    }


    int parent[];
    int size[];

    public int findparent(int u){
        if(parent[u] == u)
        return u;

        return parent[u] = findparent(parent[u]);
    }

    public boolean union(int x , int y){
        int lx = findparent(x);
        int ly = findparent(y);

        if(lx != ly){
            if(size[lx] > size[ly]){
                parent[ly] = lx;
            }
            else{
                parent[lx] = ly;

                if(size[lx] == size[ly])
                size[ly] ++;
            }

            return false;
        }
        
        //if parents same return true;
        return true;    
    }
}