The reader is advised to read all the lessons (tutorials) in this full course, in the order presented.

Problem

Given two strings, s1 and s2, check if the two strings are identical(same) or not. If the strings are identical, print "Yes", otherwise, print "No". Consider case sensitivity. Employ O(n) time and O(n) space.

Examples:

Input: s1 = "abcd", s2 = "abcd" 
Output: Yes 

Input: s1 = "", s2 = "" 
Output: Yes 

Input: s1 = "Broad-network.com", s2 = "moc.krowten-daorB" 
Output: No 

Input: s1 = "Broad", s2 = "Broad-network.com" 
Output: No 

Note:

Two empty strings are the same. An empty string should not have the space character. If the same text are in both strings and one is not in the same order as the other one, then both strings are not the same. The strings must be the same in number of characters, order of characters, and same casing for both strings.

Strategy

Compare the lengths of the strings, the characters and their order, and their casings.

Note: do not compare the variables of the two strings. Comparing their variables means comparing their references or pointers, which will hardly be the same.

Also note that since the two different cases (upper and lower) of the same character, are represented by different numbers in the computer, the program does not need extra coding to check the casing.

Program

The following program does the comparison (read through the code and comments):

areStringsSame <- function(sx, sy) {
  # Length of strings
  Nx <- nchar(sx)
  Ny <- nchar(sy)
  
  # Compare lengths first
  if (Nx != Ny) {
    return(FALSE)
  }
  
  # Compare character by character
  shorterLength <- 0
  if (Nx < Ny) {
    shorterLength <- Nx
  } else {
    shorterLength <- Ny
  }
  
  # Split strings into character vectors for indexing
    sx_chars <- utf8ToInt(sx)
    sy_chars <- utf8ToInt(sy)
  
  for (i in 1:shorterLength) {    # Avoid accessing out of bounds
    if (sx_chars[i] != sy_chars[i]) {
      return(FALSE)
    }
  }
  
  return(TRUE)
}

# Main area

s1 <- "Broad-network.com"
s2 <- "Broad-network.com"
# Call function and print answer
if (areStringsSame(s1, s2) == TRUE) {
  cat("Yes", "\n")
} else {
  cat("No", "\n")
}

sa <- "Broad"
sb <- "Broad-network.com"

# Call function and print answer
if (areStringsSame(sa, sb) == TRUE) {
  cat("Yes", "\n")
} else {
  cat("No", "\n")
}

The output is:

    Yes
    No

The time complexity is actually O(2N) for the input and function for-loops; and the space complexity is actually O(2N) for the two strings. Since the coefficient (multiplier) is normally omitted, either time complexity is given by O(N).

The time and space complexities for the actual comparing operations of the lengths and characters, of the two strings, and possible temporary variables, are ignored.

Thanks for reading.