8981. Indexes of spaces

Find the indices of the first and last space in a given string. Character indexing starts at 0.

Input. One string containing only Latin letters, punctuation marks, and spaces.

Output. Print two numbers: the index of the first space and the index of the last space in the string. If there are no spaces in the string, print -1.

Sample input 1	Sample output 1
I am programming on Python.	1 19
Sample input 2	Sample output 2
abrakadabra	-1

SOLUTION

strings

Algorithm analysis

Declare two variables:

· a is the index of the first space;

· b is the index of the last space;

Initialize them as a = b = -1. Next, iterate over the characters of the string s. If the current character is a space (s_i = ‘ ‘):

· If no spaces have been encountered before (a = -1), set a = i;

· In any case, update b = i;

After completing the iteration:

· If there are no spaces in the string (a = -1), print -1.

· Otherwise, print the indices of the first and last spaces (a and b).

Algorithm implementation

Read the input string.

getline(cin, s);

Initialize the variables a and b as the indices of the first and last spaces.

a = b = -1;

for (i = 0; i < s.size(); i++)

If the current character s_i is a space:

· If no spaces have been encountered before (a = -1), set a = i;

· Update b = i;

if (s[i] == ' ')

{

if (a == -1) a = i;

b = i;

}

If there are no spaces in the string (a = -1), print -1. Otherwise, print the indices of the first and last spaces.

if (a == -1) printf("-1\n");

else printf("%d %d\n", a, b);

Python implementation

Read the input string.

s = input()

Initialize the variables a and b as the indices of the first and last spaces.

a = b = -1

for i in range(len(s)):

If the current character s_i is a space:

· If no spaces have been encountered before (a = -1), set a = i;

· Update b = i;

if s[i] == ' ':

if a == -1: a = i

b = i

If there are no spaces in the string (a = -1), print -1. Otherwise, print the indices of the first and last spaces.

if a == -1:

print("-1")

else:

print(a, b)

Python implementation – find, rfind

Read the input string.

s = input()

Find the indices of the first and last space.

· The find function returns the index of the first occurrence of a substring in a string.

· The rfind function returns the index of the last occurrence of a substring in a string.

Both functions return -1 if the substring is not found.

a = s.find(' ')

b = s.rfind(' ')

If there are no spaces in the string (a = -1), print -1. Otherwise, print the indices of the first and last spaces.

if a == -1:

print("-1")

else:

print(a, b)