add js solution for numDistinct

problems/0115.不同的子序列.md

@@ -222,7 +222,28 @@ class SolutionDP2:
 
 Go：
 
+Javascript:
+```javascript
+const numDistinct = (s, t) => {
+    let dp = Array.from(Array(s.length + 1), () => Array(t.length +1).fill(0));
 
+    for(let i = 0; i <=s.length; i++) {
+        dp[i][0] = 1;
+    }
+    
+    for(let i = 1; i <= s.length; i++) {
+        for(let j = 1; j<= t.length; j++) {
+            if(s[i-1] === t[j-1]) {
+                dp[i][j] = dp[i-1][j-1] + dp[i-1][j];
+            } else {
+                dp[i][j] = dp[i-1][j]
+            }
+        }
+    }
+
+    return dp[s.length][t.length];
+};
+```
 
 
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