Algo naive for GeometricTrick challenge

GeometrickTrick.java

	/**
	 * Consider a string s of length n with alphabet {a,b,c}.
	 * We look for the number of different triplet (i,j,k) where 0<=i,j,k<n, satisfying!
	 * - s[i] = "a", s[j] = "b", s[k] = "c"
	 * - (j + 1)² = (i + 1)(k + 1) 
	 * @param s A string we look the triplet in
	 * @return Number of different triplets such as enonced above. 
	 */
	public static int geometricTrick(String s){
		
		//extract index for a,b and c in lists
		List<Integer> indexA = new ArrayList<>(s.length());
		List<Integer> indexB = new ArrayList<>(s.length());
		List<Integer> indexC = new ArrayList<>(s.length());
		
        //here we fill the lists created just above
		for(int i=0;i<s.length();i++){
			if(s.charAt(i)=='a')
				indexA.add(i);
			if(s.charAt(i)=='b')
				indexB.add(i);
			if(s.charAt(i)=='c')
				indexC.add(i);
		}
	
		//and then we try to find indexes satisfying the condition
		int res = 0;
		for(int tmpA:indexA)
			for(int tmpB:indexB)
				for(int tmpC:indexC)
					if(((tmpB+1)*(tmpB+1))==((tmpA+1)*(tmpC+1)))
						res++;
		
        return res;
}