Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Program to count number of distinct characters of every substring of a string in Python
Suppose we have a lowercase string s, we have to find the sum of the count of characters that are distinct in every substring of s. If the answer is very large then return result mod 10^9+7.
So, if the input is like s = "xxy", then the output will be 6, as the substrings and their counts are −
"x" : 1
"x" : 1
"y" : 1
"xx" : 0 (as "x" is not distinct)
"xy" : 2
"xxy" : 1 ("as "x" is not distinct)
To solve this, we will follow these steps −
m := 10^9 + 7
prev_seen := a new empty map
ans := 0
Define a function util() . This will take i, symbol
prev_seen[symbol] := a list with single value −1
prev := prev_seen[symbol]
insert i at the end of prev
if size of prev > 2, then
left := first element of prev and delete first element from prev
middle := prev[0], right := prev[1]
cnt :=(middle − left) *(right − middle)
ans :=(ans + cnt) mod m
for each index i and value symbol in s, do
util(i, symbol)
for each symbol in prev_seen, do
util(size of s , symbol)
return ans
Let us see the following implementation to get better understanding −
Example
class Solution:
def solve(self, s):
m = 10 ** 9 + 7
prev_seen = {}
ans = 0
def util(i, symbol):
nonlocal ans
prev = prev_seen.setdefault(symbol, [−1])
prev.append(i)
if len(prev) > 2:
left = prev.pop(0)
middle, right = prev
cnt = (middle − left) * (right − middle)
ans = (ans + cnt) % m
for i, symbol in enumerate(s):
util(i, symbol)
for symbol in prev_seen:
util(len(s), symbol)
return ans
ob = Solution()
s = "xxy"
print(ob.solve(s))Input
xxy
Output
6
160 Views
