Create 28 September Longest Bounded-Difference Subarray

28 September Longest Bounded-Difference Subarray

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+class Solution {
+  public:
+    vector<int> longestSubarray(vector<int>& arr, int x) {
+        int n = arr.size();
+        deque<int> minDq, maxDq;  // store indices
+        int l = 0, bestLen = 0, bestStart = 0;
+
+        for (int r = 0; r < n; r++) {
+            // Maintain min deque (increasing order)
+            while (!minDq.empty() && arr[minDq.back()] >= arr[r])
+                minDq.pop_back();
+            minDq.push_back(r);
+
+            // Maintain max deque (decreasing order)
+            while (!maxDq.empty() && arr[maxDq.back()] <= arr[r])
+                maxDq.pop_back();
+            maxDq.push_back(r);
+
+            // If window invalid, shrink from left
+            while (arr[maxDq.front()] - arr[minDq.front()] > x) {
+                if (minDq.front() == l) minDq.pop_front();
+                if (maxDq.front() == l) maxDq.pop_front();
+                l++;
+            }
+
+            // Update best window
+            if (r - l + 1 > bestLen) {
+                bestLen = r - l + 1;
+                bestStart = l;
+            }
+        }
+
+        return vector<int>(arr.begin() + bestStart, arr.begin() + bestStart + bestLen);
+    }
+};