feat: Add R program to find longest substring without repeating characters (#163)

Author: sgindeed

string_manipulation/longest.substring.no.repeat.R

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+# Longest Substring Without Repeating Characters in R
+# Author: sgindeed
+# Description: Finds the length of the longest substring without repeating characters
+
+# Ask for user input
+input.string <- readline(prompt = "Enter a string: ")
+
+# Convert the string to lowercase for case-insensitive processing (optional)
+clean.string <- tolower(input.string)
+
+# Split string into characters
+chars <- strsplit(clean.string, "")[[1]]
+
+# Initialize variables
+hash.table <- list()  # stores last index of characters
+max.length <- 0
+start <- 1  # start of current window
+
+# Iterate over characters
+for (i in seq_along(chars)) {
+  char <- chars[i]
+  
+  # If character was seen before and is inside current window
+  if (!is.null(hash.table[[char]]) && hash.table[[char]] >= start) {
+    start <- hash.table[[char]] + 1  # move start to one after previous occurrence
+  }
+  
+  # Update last seen index of the character
+  hash.table[[char]] <- i
+  
+  # Update max length
+  current.length <- i - start + 1
+  if (current.length > max.length) {
+    max.length <- current.length
+  }
+}
+
+# Display the result
+cat("Length of the longest substring without repeating characters:", max.length, "\n")