Longest Subarray Length

JavaView on GFG

Time: O(n)

Space: O(n)

Problem Overview

Find length of longest subarray with equal number of 0s and 1s.

See our study guide for structured GFG and LeetCode practice.

Intuition

Find length of longest subarray with equal number of 0s and 1s. Prefix sum + hashmap.

Algorithm

1Encode 0 as -1. Find longest subarray with sum 0 using prefix sum and first-occurrence hashmap.

Common Pitfalls

• Same as LC 525. Map prefix sum to first index. When same prefix sum seen again: span is a valid subarray.

Longest Subarray Length.java

Java

// Approach: Sliding window with HashMap tracking first occurrence of prefix state.
// Time: O(n) Space: O(n)
import java.util.*;

class Solution {
    public static int longestSubarray(int[] arr) {
        int n = arr.length;
        int maxLen = 0;

        Stack<Integer> st = new Stack<>();

        for (int i = 0; i <= n; i++) {
            int nge = (i == n ? Integer.MAX_VALUE : arr[i]);

            while (!st.isEmpty() && arr[st.peek()] < nge) {
                int curr = arr[st.pop()];
                int len = st.isEmpty() ? i : i - st.peek() - 1;

                if (len >= curr)
                    maxLen = Math.max(maxLen, len);
            }

            st.push(i);
        }

        return maxLen;

    }
}

Was this solution helpful?