added recursion example with easy solution for beginners

Recursion/sum_of_1d_array.js

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+/*
+  NOTE: The provided solution is not copied
+
+
+  RECURSION Example in JavaScript
+
+  Problem: sum_of_1d_array ( from leetcode )
+
+  Explanation for problem: {
+    Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]).
+    Return the running sum of nums.
+  }
+
+  Demo:{
+    Input: nums = [1,2,3,4]
+    Output: [1,3,6,10]
+    Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4].
+  }
+  
+*/
+
+// Test case [1,2,3,4]
+// Expected output [1,3,6,10]
+
+const array = [1, 2, 3, 4];
+
+// Recursive Solution
+
+const runningSum = (nums) => {
+  let result = [nums[0]];
+  const recursive = (loop) => {
+    if (nums.length <= loop) return;
+    else result.push(nums[loop] + result[loop - 1]);
+    recursive(loop + 1);
+  };
+  recursive(1);
+  return result;
+};
+
+runningSum(array); // function call
+
+/*
+  Funtion runningSum takes an array of numbers as an argument
+  returns an array of running sum of given array
+
+  Note: recursive functions starts from index 1 of given array because we already assign index 0 value to result at the start
+  recursive function runs until the index given to recursive function is greater than equal to the length or array given to runningSum function
+*/