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# Program to find largest substring between two equal characters in Python

Suppose we have a string s, we have to find the length of the longest substring between two equal letters or elements, excluding the two characters. If we cannot find such substring, then return -1.

So, if the input is like s = "level", then the output will be 3 as optimal substrings can be either "lev" or "vel".

To solve this, we will follow these steps −

memo := a new map

for i in range 0 to size of s - 1, do

if s[i] is in memo, then

insert i at the end of memo[s[i]]

otherwise,

memo[s[i]] := a list with only one element i

best := 0

for each key in memo, do

best := maximum of best and (last element of memo[key] - first element of memo[key])

return best - 1

## Example (Python)

def solve(s): memo = {} for i in range(len(s)): if s[i] in memo: memo[s[i]].append(i) else: memo[s[i]] = [i] best = 0 for key in memo: best = max(best, memo[key][-1] - memo[key][0]) return best - 1 s = "level" print(solve(s))

## Input

"level"

## Output

3

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