subarraySum

subarraySum.js

@@ -0,0 +1,34 @@
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ * 
+ * Intution:
+ * I am using prefix sum plus hashMap approach in here.
+ * At each index i am calculating the currSum and check if the diff between the k and currSum exists before in the array. If yes, i am incrementing the count by the value length.
+ * And if the currSum is in the map then adding the new index to the array, otherwise creating the array with the currIndex.
+ * Time Complexity: O(n);
+ * Space Complexity: O(n)
+ */
+var subarraySum = function (nums, k) {
+    let preFixMap = new Map();
+    let currSum = 0;
+    // set 0 with -1 to handle the edge case
+    preFixMap.set(0, [-1]);
+    let count = 0;
+    for (let i = 0; i < nums.length; i++) {
+        currSum += nums[i];
+        const diff = currSum - k;
+        if (preFixMap.has(diff)) {
+            const currAssignedVal = preFixMap.get(diff);
+            count += currAssignedVal.length;
+        }
+        if (preFixMap.has(currSum)) {
+            const currArr = preFixMap.get(currSum);
+            currArr.push(i);
+        } else {
+            preFixMap.set(currSum, [i]);
+        }
+    }
+    return count;
+};