Create 940-distinct-subsequences-ii.js

Author: everthis

940-distinct-subsequences-ii.js

@@ -0,0 +1,30 @@
+/**
+ * @param {string} S
+ * @return {number}
+ */
+const distinctSubseqII = function(S) {
+  // let end = new Array(26).fill(0), res = 0, added = 0, mod = 10 ** 9 + 7;
+  // const aCode = ('a').charCodeAt(0)
+  // for (let c of S) {
+  //     added = (res + 1 - end[c.charCodeAt(0) - aCode]) % mod;
+  //     res = (res + added) % mod;
+  //     end[c.charCodeAt(0) - aCode] = (end[c.charCodeAt(0) - aCode] + added) % mod;
+  // }
+  // return (res + mod) % mod;
+  const m = new Map(),
+    dp = [1],
+    M = 1000000007
+  for (let i = 0; i < S.length; i++) {
+    const c = S.charAt(i)
+    let prev = 0
+    if (m.has(c)) {
+      prev = dp[m.get(c)]
+    }
+    m.set(c, i)
+    dp.push((((dp[i] * 2) % M) - prev) % M)
+    if (dp[i + 1] < 0) {
+      dp[i + 1] += M
+    }
+  }
+  return dp[S.length] - 1
+}