Added 1D DP JS solution for problem 115

Author: imaginate

javascript/115-Distinct-Subsequences.js

@@ -0,0 +1,29 @@
+/**
+ * @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(tLen).fill(0);
+    
+    for (let r = sLen - 1; r >= 0; --r) {
+        let prev = 1;
+        for (let c = tLen - 1; c >= 0; --c) {
+            const curr = cache[c];
+            if (s[r] === t[c]) {
+                cache[c] += prev;
+            }
+            prev = curr;
+        }
+    }
+    
+    return cache[0];
+}