Added 2D DP JS solution for problem 115

Author: imaginate

javascript/115-Distinct-Subsequences.js

@@ -27,3 +27,38 @@ function numDistinct(s, t) {
 
     return cache[0];
 }
+
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {number}
+ */
+function numDistinct(s, t) {
+    
+    const sLen = s.length;
+    const tLen = t.length;
+    
+    if (sLen < tLen) {
+        return 0;
+    }
+    
+    const cache = new Array(sLen + 1).fill()
+        .map(() => new Array(tLen + 1));
+    
+    cache[sLen].fill(0);
+    for (let r = 0; r <= sLen; ++r) {
+        cache[r][tLen] = 1;
+    }
+    
+    for (let r = sLen - 1; r >= 0; --r) {
+        for (let c = tLen - 1; c >= 0; --c) {
+            cache[r][c] = cache[r + 1][c] + (
+                s[r] === t[c]
+                    ? cache[r + 1][c + 1]
+                    : 0
+            );
+        }
+    }
+    
+    return cache[0][0];
+}