Create 1960-maximum-product-of-the-length-of-two-palindromic-substrings.js

Author: everthis

1960-maximum-product-of-the-length-of-two-palindromic-substrings.js

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+/**
+ * @param {string} s
+ * @return {number}
+ */
+const maxProduct = function (s) {
+  const t1 = helper(s),
+    t2 = helper(reverse(s))
+  let res = 0
+  for (let n = s.length, i = 0, j = n - 2; i < n - 1; ++i, --j)
+    res = Math.max(res, t1[i] * t2[j])
+
+  return res
+}
+function reverse(s) {
+  return [...s].reverse().join('')
+}
+function helper(s) {
+  const man = manachers(s).filter(
+    (e, i, ar) => i >= 2 && i < ar.length - 2 && i % 2 === 0
+  )
+  const n = s.length,
+    { max } = Math
+  const ints = man.map((e, i) => [i - ~~(e / 2), i + ~~(e / 2)])
+  const arr = Array(n).fill(0)
+  for (const [a, b] of ints) {
+    arr[b] = max(arr[b], b - a + 1)
+  }
+  for (let i = n - 2; i >= 0; i--) {
+    arr[i] = max(arr[i], arr[i + 1] - 2)
+  }
+  let tmp = 0
+  for (let i = 0; i < n; i++) {
+    if (arr[i] > tmp) {
+      tmp = arr[i]
+    } else arr[i] = tmp
+  }
+  return arr
+}
+function manachers(s) {
+  const str = `@#${s.split('').join('#')}#$`
+  const arr = Array(str.length).fill(0)
+
+  let center = 0,
+    right = 0
+  for (let i = 1, n = str.length; i < n - 1; i++) {
+    if (i < right) {
+      arr[i] = Math.min(right - i, arr[2 * center - i])
+    }
+    while (str[i + arr[i] + 1] === str[i - arr[i] - 1]) {
+      arr[i] += 1
+    }
+    if (i + arr[i] > right) {
+      center = i
+      right = i + arr[i]
+    }
+  }
+
+  return arr
+}