CompetitiveCode

create hashmap 
        Map<Integer, Integer> map = new HashMap<>();
        map.containsKey(target)
        map.get(target)
iterate over each entry in a Map
        Map<String, String> map = ...
        for (Map.Entry<String, String> entry : map.entrySet())
        {
            System.out.println(entry.getKey() + "/" + entry.getValue());
        }
binary search O(log n)
        private int bsearch(int[] A, int key, int start) {
        int L = start, R = A.length - 1;
        while (L < R) {
        int M = (L + R) / 2;
        if (A[M] < key) {
        L = M + 1;
        } else {
        R = M;
        }
        }
        return (L == R && A[L] == key) ? L : -1;
        }
substring() 
        is used for getting a substring of a particular String. There are two variants of this method
java.lang.StringBuilder.append()
        used to append the string representation of some argument to the sequence.
        There are 13 ways/forms in which the append() method can be used by the passing of various types of arguments