package main
import (
  "fmt"
  "strings"
)
/*
Given a string s, return the longest palindromic substring in s.

Example 1:

Input: s = "babad"
Output: "bab"
Note: "aba" is also a valid answer.
Example 2:

Input: s = "cbbd"
Output: "bb"
Example 3:

Input: s = "a"
Output: "a"
Example 4:

Input: s = "ac"
Output: "a"
 

Constraints:

1 <= s.length <= 1000
s consist of only digits and English letters.
*/

/*
  Hints: If the string is 2 characters and they are both the same character then it is a palindrome (ie: aa or 11)

  So you can use create a table to calculate a table where if table[i+1][j-1] is true and string[i+1] == string[j-1] 
  then the substring string is a palindrome

  You can see that i+1, j-1 is like two pointers with one going forward and the other going backwards


    a b a 
  a 0 0 1
  b 0 1 0
  a 1 0 1
*/
func longestPalindrome(s string) string {
  /*
    If string s has a len = 1 then the longest palindrome is s

    If string s has len = 2 and the two characters are the same then the longest palindrome is s
  */

  var n = len(s)

  if n == 1 {
    return s 
  }

  if n == 2 && s[0] == s[1] {
    return s
  }

  // Generate memory table table[i][i] = true 
  var output string
  dp := make([][]bool, n)
  for i:= 0; i < n - 1; i++ {
    dp[i] = make([]bool, n)
    dp[i][i] = true
  }

  // Need to do this to access by index
  // see https://stackoverflow.com/questions/15018545/how-to-index-characters-in-a-golang-string
  strarr := strings.Split(s, "")
  // Also check for palidrome where length == 2 using s[i] == s[i+1] 
  for i := 0; i < n - 1; i++ {
    if (strarr[i] == strarr[i+1]) {
      dp[i][i+1] = true
      output = s[i:i+1]
    }
  }

   // n = 5 
   // i = 2; x = 0; y = 1

  // Find substring where n > 2
  for i := 2; i < n - 1; i++ {
    for x := 0; x < n - i; x++ {
      // starting at x find the end idx (len substring - 1 )
      y :=  x + i - 1 
      if (dp[x+1][y-1] && strarr[x] == strarr[y]) {
        output = s[x:(y+1)] 
      }
    }
  }
  return output
}

func main () {
  fmt.Println(longestPalindrome("babad"))
}