gistfile1.java

package com.stackoverflow;

import java.util.Arrays;
import java.util.Comparator;

public class ContSubArray {
	public static void main(String[] args) {
		
		int[] array = 
					//{10, 5, 3, 1, 4, 2, 8, 7};
					//{10, 5, 24, 3, 1, 4, 2, 8, 7};
					//{10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, -1};
			{4, 5, 1, 5, 7, 6, 8, 4, 1};
				
		E[] ext = new E[array.length];
		for (int i = 0; i < array.length; i++) {
			E e = new E();
			ext[i] = e;
			e.e = array[i];
			e.idx = i;
		}
		
		System.out.println("Input: " + Arrays.toString(array));
		System.out.println("Length: " + find(ext));
	}
	
	static int find(E[] array) {
		// sort input (can be done in O(n) for integers)
		Arrays.sort(array, new Comparator<E>() {
			@Override
			public int compare(E o1, E o2) {
				return o1.e - o2.e;
			}
		});
		
		System.out.println(Arrays.toString(array));
		
		int maxN = 1; 
		int sum = 0;
		int groupMin = Integer.MAX_VALUE;
		int curN = 0;
		int prev = -1; // none
		for (int i = 0; i < array.length; i++) {
			if (curN == 0) {
				sum = array[i].idx;
				groupMin = array[i].idx;
				prev = array[i].e;
				curN++;
			} else {
				if (array[i].e != prev + 1) {
					curN = 1;
					prev = array[i].e;
					sum = array[i].idx;
					groupMin = array[i].idx;
				} else { // continuous
					groupMin = Math.min(groupMin, array[i].idx);
					curN++;
					sum += array[i].idx;
					int estSum = estSum(groupMin, curN);
					prev = array[i].e;
					if (estSum == sum) {
						maxN = Math.max(curN, maxN);
					}
				}
			}
		}
		
		return maxN;
	}
	
	static int estSum(int a, int n) {
		return a * n + (n * (n - 1)) / 2;
	}
	
}

class E {
	int e;
	int idx;
	
	@Override
	public String toString() {
		return "[" + e + ", " + idx + "]";
	}
}

@mishadoff
This won't work for arrays like this [4,100,3,2,1000,1]. Your algo will check for [1->5,2->3,3->2,4->0] and see that this isn't possible and give 1 as final answer. But [2->3,3->2] is valid and the answer should be 2
https://stackoverflow.com/a/15987767/5524175