Create maximum-good-subarray-sum.cpp

Author: kamyu104

C++/maximum-good-subarray-sum.cpp

@@ -0,0 +1,25 @@
+// Time:  O(n)
+// Space: O(n)
+
+// prefix sum
+class Solution {
+public:
+    long long maximumSubarraySum(vector<int>& nums, int k) {
+        const auto NEG_INF = numeric_limits<int64_t>::min();
+        const auto POS_INF = numeric_limits<int64_t>::max();
+
+        unordered_map<int, int64_t> prefix;
+        int64_t result = NEG_INF, curr = 0;
+        for (const auto& x : nums) {
+            prefix[x] = min(prefix.count(x) ? prefix[x] : POS_INF, curr);
+            curr += x;
+            if (prefix.count(x - k)) {
+                result = max(result, curr - prefix[x - k]);
+            }
+            if (prefix.count(x + k)) {
+                result = max(result, curr - prefix[x + k]);
+            }
+        }
+        return result != NEG_INF ? result : 0;
+    }
+};