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5. Longest Palindromic Substring
Medium
Given a string s, return the longest palindromic substring in s.
Example 1:
Input: s = “babad”
Output: “bab”
Explanation: “aba” is also a valid answer.
Example 2:
Input: s = “cbbd”
Output: “bb”
Constraints:
1 <= s.length <= 1000sconsist of only digits and English letters.
Solution
function longestPalindrome(s: string): string {
const newStr: string[] = new Array(s.length * 2 + 1)
newStr[0] = '#'
for (let i = 0; i < s.length; i++) {
newStr[2 * i + 1] = s.charAt(i)
newStr[2 * i + 2] = '#'
}
const dp: number[] = new Array(newStr.length)
let friendCenter: number = 0
let friendRadius: number = 0
let lpsCenter: number = 0
let lpsRadius: number = 0
for (let i = 0; i < newStr.length; i++) {
dp[i] =
friendCenter + friendRadius > i ? Math.min(dp[2 * friendCenter - i], friendCenter + friendRadius - i) : 1
while (i + dp[i] < newStr.length && i - dp[i] >= 0 && newStr[i + dp[i]] === newStr[i - dp[i]]) {
dp[i]++
}
if (friendCenter + friendRadius < i + dp[i]) {
friendCenter = i
friendRadius = dp[i]
}
if (lpsRadius < dp[i]) {
lpsCenter = i
lpsRadius = dp[i]
}
}
return s.substring((lpsCenter - lpsRadius + 1) / 2, (lpsCenter + lpsRadius - 1) / 2)
}
export { longestPalindrome }