Solution.java

class Solution {
    public boolean equationsPossible(String[] equations) {
        HashMap<Character, ArrayList<Character>> equalGraph = new HashMap<>();
            
        for(String equation: equations)
        {
            if(equation.charAt(1)=='=')
            {
                Character var1 = equation.charAt(0);  
                Character var2 = equation.charAt(3);
                
                if(var1.equals(var2)) 
                { 
                    continue;
                }
                
                
                if(!equalGraph.containsKey(var1))
                {
                    equalGraph.put(var1, new ArrayList<>());
                }
                
                List<Character> edges = equalGraph.get(var1);
                edges.add(var2);
                
                if(!equalGraph.containsKey(var2))
                {
                    equalGraph.put(var2, new ArrayList<>());
                }
                List<Character> edges2 = equalGraph.get(var2);
                edges2.add(var1);
                    
            }
        }
        
        for(String equation: equations)
        {
            if(equation.charAt(1)=='!')
            {
                char var1 = equation.charAt(0);  
                char var2 = equation.charAt(3);
            
                if(var1 == var2) return false;
                
                if(!equalGraph.containsKey(var1) || !equalGraph.containsKey(var2))
                {
                   continue;
                }
                
                //BFS
                boolean[] visited= new boolean[26];
                visited[var1-'a'] = true;
                ArrayDeque<Character> queue = new ArrayDeque<>();
                queue.add(var1);
                
                while(!queue.isEmpty())
                {
                    char iter = queue.poll();
                    visited[iter-'a'] = true;
                    ArrayList<Character> list = equalGraph.get(iter);
                    for(Character ch: list)
                    {
                        if(ch.equals(var2))
                        {
                            return false;
                        }
                        if(!visited[ch-'a'])
                        {
                            queue.add(ch);
                        }
                    }
                }
            }
        }
        
        return true;
        
    }
}