solution.java

import java.util.*;

class Solution {
    public static int longestSubarray(int[] arr) {
        int n = arr.length;
        int[] left = new int[n];
        int[] right = new int[n];
        Deque<Integer> st = new ArrayDeque<>();

        for (int i = 0; i < n; i++) {
            while (!st.isEmpty() && arr[st.peek()] <= arr[i]) {
                st.pop();
            }
            left[i] = st.isEmpty() ? -1 : st.peek();
            st.push(i);
        }

        st.clear();

        for (int i = n - 1; i >= 0; i--) {
            while (!st.isEmpty() && arr[st.peek()] <= arr[i]) {
                st.pop();
            }
            right[i] = st.isEmpty() ? n : st.peek();
            st.push(i);
        }

        int ans = 0;
        for (int i = 0; i < n; i++) {
            int length = right[i] - left[i] - 1;
            if (arr[i] <= length) {
                ans = Math.max(ans, length);
            }
        }

        return ans;
    }
}