Added memo JS solution for problem 97

Author: imaginate

javascript/97-Interleaving-String.js

@@ -0,0 +1,49 @@
+/**
+ * @param {string} s1
+ * @param {string} s2
+ * @param {string} s3
+ * @return {boolean}
+ */
+function isInterleave(s1, s2, s3) {
+    
+    const l1 = s1.length;
+    const l2 = s2.length;
+    const l3 = s3.length;
+    
+    if (l1 + l2 !== l3) {
+        return false;
+    }
+    if (!s1 || !s2 || !s3) {
+        return (!s1 && !s2 && !s3) || (
+            s1
+                ? s1 === s3
+                : s2 === s3
+        );
+    }
+    
+    const seen = new Array(l1 + 1).fill()
+        .map(() => new Array(l2 + 1));
+    return checkStrings();
+    
+    /**
+     * @param {number=} i = `0`
+     * @param {number=} j = `0`
+     * @param {number=} k = `0`
+     * @return {boolean}
+     */
+    function checkStrings(i = 0, j = 0, k = 0) {
+        return k === l3 || (
+            seen[i][j] !== undefined
+                ? seen[i][j]
+                : seen[i][j] = (
+                    i < l1
+                    && s1[i] === s3[k]
+                    && checkStrings(i + 1, j, k + 1)
+                ) || (
+                    j < l2
+                    && s2[j] === s3[k]
+                    && checkStrings(i, j + 1, k + 1)
+                )
+        );
+    }
+}