Doubt on the code of string hashing

#1

long long compute_hash(string const& s) {
const int p = 31;
const int m = 1e9 + 9;
long long hash_value = 0;
long long p_pow = 1;
for (char c : s) {
hash_value = (hash_value + (c - ‘a’ + 1) * p_pow) % m;
p_pow = (p_pow * p) % m;
}
return hash_value;
}
This is the code for the string hashing ,What is the significance of this expression “(c - ‘a’ + 1) '”??

#2

hello @Somasree

it converts character to int .

for example
if character c is ‘a’ then it will give 1
if character c is ‘b’ then it will give 2
if character c is ‘c’ then it will give 3
if character c is ‘d’ then it will give 4
so on…

#3

ok thank u so much :grinning:

#4

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#5

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image1920×1080 363 KB

Please explain to me how the ans is 45.
Is there a formula n*(n-1)/2. used here

#6

yeah . . …
if we have n vertices, then we can pick two vertices and draw an edge between then. that why nC2 = n *(n-1)/2

#7

ok understood thank u :smiley: