Python Program To Find Length Of The Longest Substring Without Repeating Characters

# Python3 program to find the length
# of the longest substring without
# repeating characters

# This functionr eturns true if all
# characters in strr[i..j] are 
# distinct, otherwise returns false
def areDistinct(strr, i, j):

    # Note : Default values in visited are false
    visited = [0] * (26)

    for k in range(i, j + 1):
        if (visited[ord(strr[k]) - 
                   ord('a')] == True):
            return False
            
        visited[ord(strr[k]) -
                ord('a')] = True

    return True

# Returns length of the longest substring
# with all distinct characters.
def longestUniqueSubsttr(strr):
    
    n = len(strr)
    
    # Result
    res = 0 
    
    for i in range(n):
        for j in range(i, n):
            if (areDistinct(strr, i, j)):
                res = max(res, j - i + 1)
                
    return res

# Driver code
if __name__ == '__main__':
    
    strr = "geeksforgeeks"
    print("The input is ", strr)
    
    len = longestUniqueSubsttr(strr)
    print("The length of the longest "
          "non-repeating character substring is ", len)

# This code is contributed by mohit kumar 29

# Python3 program to find the 
# length of the longest substring
# without repeating characters
def longestUniqueSubsttr(str):
    
    n = len(str)
    
    # Result
    res = 0 
 
    for i in range(n):
         
        # Note : Default values in 
        # visited are false
        visited = [0] * 256   
 
        for j in range(i, n):
 
            # If current character is visited
            # Break the loop
            if (visited[ord(str[j])] == True):
                break
 
            # Else update the result if
            # this window is larger, and mark
            # current character as visited.
            else:
                res = max(res, j - i + 1)
                visited[ord(str[j])] = True
            
        # Remove the first character of previous
        # window
        visited[ord(str[i])] = False
    
    return res

# Driver code
str = "geeksforgeeks"
print("The input is ", str)

len = longestUniqueSubsttr(str)
print("The length of the longest " 
      "non-repeating character substring is ", len)

# This code is contributed by sanjoy_62

# Python3 program to find the length
# of the longest substring
# without repeating characters
def longestUniqueSubsttr(string):

    # last index of every character
    last_idx = {}
    max_len = 0

    # starting index of current 
    # window to calculate max_len
    start_idx = 0

    for i in range(0, len(string)):
      
        # Find the last index of str[i]
        # Update start_idx (starting index of current window)
        # as maximum of current value of start_idx and last
        # index plus 1
        if string[i] in last_idx:
            start_idx = max(start_idx, last_idx[string[i]] + 1)

        # Update result if we get a larger window
        max_len = max(max_len, i-start_idx + 1)

        # Update last index of current char.
        last_idx[string[i]] = i

    return max_len


# Driver program to test the above function
string = "geeksforgeeks"
print("The input string is " + string)
length = longestUniqueSubsttr(string)
print("The length of the longest non-repeating character" +
      " substring is " + str(length))

# Here, we are planning to implement a simple sliding window methodology
 
def longestUniqueSubsttr(string):
     
    # Creating a set to store the last positions of occurrence
    seen = {}
    maximum_length = 0
 
    # starting the initial point of window to index 0
    start = 0 
     
    for end in range(len(string)):
 
        # Checking if we have already seen the element or not
        if string[end] in seen:

            # If we have seen the number, move the start pointer
            # to position after the last occurrence
            start = max(start, seen[string[end]] + 1)
 
        # Updating the last seen value of the character
        seen[string[end]] = end
        maximum_length = max(maximum_length, end-start + 1)
    return maximum_length
 
# Driver Code
string = "geeksforgeeks"
print("The input string is", string)
length = longestUniqueSubsttr(string)
print("The length of the longest non-repeating character substring is", length)