import java.util.HashMap; public class StarHash { public static void main(String[] args) { String x = "*##*###**"; char[] c = x.toCharArray(); int[] q = new int[c.length]; for(int i = 0; i < c.length; i++) { if(c[i] == '*') { q[i] = -1; } else { q[i] = 1; } } int sum = 0; int longestFromBegin = 0; for(int i = 0; i < q.length; i++) { sum += q[i]; if(sum == 0) longestFromBegin = i; q[i] = sum; } HashMap m = new HashMap(); // find substring - find all same int max = 0; for(int i = 0; i < q.length; i++) { if(!m.containsKey(q[i])) { m.put(q[i], i); } else { // store max max = Math.max(max, i - m.get(q[i])); } } System.out.println("Max: " + max); } }