Create longest-well-performing-interval.cpp

Author: kamyu104

C++/longest-well-performing-interval.cpp

@@ -0,0 +1,25 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    int longestWPI(vector<int>& hours) {
+        int result = 0, accu = 0;
+        unordered_map<int, int> lookup;
+        for (int i = 0; i < hours.size(); ++i) {
+            accu += (hours[i] > 8) ? 1 : -1;
+            if (accu > 0) {
+                result = i + 1;
+            } else if (lookup.count(accu - 1)) {
+                // lookup[accu-1] is the leftmost idx with smaller accu,
+                // because from 1 to some positive k,
+                // lookup[accu-i] is a strickly increasing sequence
+                result = max(result, i - lookup[accu - 1]);
+            }
+            if (!lookup.count(accu)) {
+                lookup[accu] = i;
+            }
+        }
+        return result;
+    }
+};