Longest Consecutively Increasing Substring - Facebook Top Interview Questions


Problem Statement :


You are given a string s containing lowercase alphabet characters as well as "?". 

For each "?" you must either delete it or replace it with any lowercase alphabet character.

Return the length of the longest consecutively increasing substring that starts with "a".

Constraints


1 ≤ n ≤ 100,000 where n is the length of s

Example 1

Input

s = "bca???de"

Output

5

Explanation

We can turn s into "bcabcde" and "abcde" is the longest consecutively increasing substring that starts 
with "a"



Example 2

Input

s = "zyx"

Output

0

Explanation

No substring here starts with "a"


Solution :



title-img 




                        Solution in C++ :

int solve(string s) {
    int i, j, n = s.size(), ret = 0;
    vector<vector<int>> dp(n, vector<int>(26, 0));
    for (i = 0; i < n; i++) {
        if (s[i] == 'a')
            dp[i][0] = 1;
        else if (s[i] == '?') {
            dp[i][0] = 1;
            for (j = 1; i && j < 26; j++) {
                dp[i][j] = dp[i - 1][j];
                if (dp[i - 1][j - 1]) dp[i][j] = max(dp[i][j], dp[i - 1][j - 1] + 1);
            }
        } else {
            j = s[i] - 'a';
            if (i && dp[i - 1][j - 1]) dp[i][j] = max(dp[i][j], dp[i - 1][j - 1] + 1);
        }
    }
    for (i = 0; i < n; i++)
        for (j = 0; j < 26; j++) ret = max(ret, dp[i][j]);
    return ret;
}
                    


                        Solution in Java :

import java.util.*;

class Solution {
    public int solve(String s) {
        dp = new Integer[s.length()][256];

        int res = 0;
        for (int i = 0; i < s.length(); i++)
            if (s.charAt(i) == 'a' || s.charAt(i) == '?')
                res = Math.max(res, lci(s, i, (char) ('a' - 1)));

        return res;
    }
    Integer[][] dp;
    private int lci(String s, int curr, char prev) {
        if (curr >= s.length() || (s.charAt(curr) != '?' && s.charAt(curr) != prev + 1)
            || prev == 'z')
            return 0;
        if (dp[curr][prev] != null)
            return dp[curr][prev];

        if (s.charAt(curr) == '?')
            return dp[curr][prev] =
                       Math.max(1 + lci(s, curr + 1, (char) (prev + 1)), lci(s, curr + 1, prev));
        return dp[curr][prev] = 1 + lci(s, curr + 1, s.charAt(curr));
    }
}
                    


                        Solution in Python : 
                            
class Solution:
    def solve(self, s):
        idx = 0
        ans = count = 0

        @cache
        def find(idx, exp):
            if ord(exp) == 123 or idx >= len(s):
                return 0
            if s[idx] == exp or s[idx] == "?":
                if s[idx] == "?":
                    return max(1 + find(idx + 1, chr(ord(exp) + 1)), find(idx + 1, exp))
                return 1 + find(idx + 1, chr(ord(exp) + 1))
            return 0

        while idx < len(s):
            if s[idx] == "a" or s[idx] == "?":
                ans = max(find(idx, "a"), ans)
            idx += 1
        return ans


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