add: 最长回文字符串

src/string/longest-palindromic-substring.js

@@ -0,0 +1,36 @@
+export const longestPalindrome = function (s) {
+  if (!s || !s.trim()) return ''
+  if (s.length === 1) return s
+  if (s.length === 2) return s[0] === s[1] ? s[0] + s[1] : s[1]
+  let result = ''
+  /**
+  *扩散坐标
+  */
+  const calPalindromeIndex = function (left, right, s) {
+    const len = s.length
+    while (left >= 0 && right < len && s[left] === s[right]) {
+      left--
+      right++
+    }
+    return { left: left + 1, right: right }
+  }
+  for (let i = 0, len = s.length; i < len; i++) {
+    let even = ''
+    let odd = ''
+    if (s[i] === s[i + 1]) {
+      // 经过当前位与下一位判断已构成回文，扩散位直接从下一位开始，可以提速
+      const evenIndex = calPalindromeIndex(i - 1, i + 2, s)
+      even = s.slice(evenIndex.left, evenIndex.right)
+    }
+    const oddIndex = calPalindromeIndex(i - 1, i + 1, s)
+    odd = s.slice(oddIndex.left, oddIndex.right)
+    const re = odd.length > even.length ? odd : even
+    result = result.length > re.length ? result : re
+  }
+  return result
+}
+
+// 作者：liu-zi-qian-2
+// 链接：https://leetcode-cn.com/problems/longest-palindromic-substring/solution/5-zui-chang-hui-wen-zi-chuan-by-liu-zi-qian-2/
+// 来源：力扣（LeetCode）
+// 著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。