Create 2484-count-palindromic-subsequences.js

Author: everthis

2484-count-palindromic-subsequences.js

@@ -0,0 +1,31 @@
+const initialize2DArray = (n, m) => {
+  let d = []
+  for (let i = 0; i < n; i++) {
+    let t = Array(m).fill(0)
+    d.push(t)
+  }
+  return d
+}
+
+const mod = 1e9 + 7
+/**
+ * @param {string} s
+ * @return {number}
+ */
+const countPalindromes = (s) => {
+  let res = 0,
+    n = s.length,
+    cnt = Array(10).fill(0)
+  for (let i = 0; i < n; i++) {
+    let tot = 0
+    for (let j = n - 1; j > i; j--) {
+      if (s[i] == s[j]) {
+        res += tot * (j - i - 1)
+        res %= mod
+      }
+      tot += cnt[s[j] - "0"]
+    }
+    cnt[s[i] - "0"]++
+  }
+  return res
+}