Q22 Palindromic Substrings - LeetCode 647

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Fri Mar 24 2023 09:11:36 GMT+0000 (Coordinated Universal Time)

Saved by @Ayush_dabas07

class Solution {
    public int countSubstrings(String s) {
        /* question of DP gap strategy vid 32 of dp playlist
        
        1)making a boolean array for checking pallindrome by keeping start
        points on coloumn and end points on rows
        
        2)travelling the upper triangle only ,where 0th diagnol represents
        substring with 0 gap that is that element itself 

        3) handling for 0 ,1 gap which are trivial case then handling for 
        2 onwards , where we will check extremities and if inside string is 
        also pallindrome by checking diagnolly behind
        */

        //1
        boolean dp[][] = new boolean[s.length()][s.length()];
        int count = 0 , n = s.length();

        //2

        for(int gap = 0 ; gap < n ; gap ++){
            
            //every diagnol ends at last coloumn,so this loop runs from first
            //row till last coloumn
            for(int i = 0 , j = gap ; j < n ; i++ , j++){

                //handling for 0 gap diagnol -> all are true
                if(gap == 0 ){
                    dp[i][j] = true;
                    count++;
                }
                


                //handling for 1 gap diagnol -> check if both chars are equal
                else if(gap == 1){
                    if(s.charAt(i) == s.charAt(j)){
                        dp[i][j] = true;
                        count++;
                    }
                    
                }


                //3
                else{
                    
                    if(s.charAt(i) == s.charAt(j) && dp[i+1][j-1] == true){
                        dp[i][j] = true;
                        count++;
                    }
                    
                }
            }
        }

        return count;
        
    }
}

https://leetcode.com/problems/palindromic-substrings/

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DP level 2

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