FourSumTreeMap.java

class FourSumTreeMap {
    public static void main(String[] args) {
        
    }
    
    public static List<List<Integer>> fourSum(int[] num, int target) {
        /**
         * regard two integers as a pair
         */
        class Pair {
            int a;
            int ai;
            int b;
            int bi;
            
            public Pair(int a, int ai, int b, int bi) {
                this.a = a;
                this.ai = ai;
                this.b = b;
                this.bi = bi;
            }
            
            boolean same(Pair p) {
                return p != null && p.a == a && p.b == b;
            }
        }
        
        
    }
}