Find the character in first string that is present at minimum index in second string in Python

Suppose we have a string str and another string patt, we need to find the character in patt that is present at the minimum index in str. If no character from patt is present in str, then return -1.

For example, if str = "helloworld" and patt = "wor", the output will be 'o' because 'o' appears at index 4, which is the smallest index among all characters from patt that exist in str.

Algorithm Steps

To solve this problem, we follow these steps ?

• Initialize minimum_index to a large value

• For each character in patt, find its first occurrence in str

• Keep track of the minimum index found so far

• Return the character at minimum index, or -1 if no character is found

Implementation

Let us see the implementation to get better understanding ?

def get_min_index_char(str_input, patt):
    minimum_index = 10**9
    
    for i in range(len(patt)):
        for j in range(len(str_input)):
            if (patt[i] == str_input[j] and j < minimum_index):
                minimum_index = j
                break
    
    if (minimum_index != 10**9):
        return str_input[minimum_index]
    else:
        return -1

# Test the function
str_input = "helloworld"
patt = "wor"
result = get_min_index_char(str_input, patt)
print(f"Character at minimum index: {result}")

The output of the above code is ?

Character at minimum index: o

How It Works

In the example above:

• 'w' is found at index 5 in "helloworld"

• 'o' is found at index 4 in "helloworld"

• 'r' is found at index 8 in "helloworld"

Since index 4 is the minimum among these positions, the function returns 'o'.

Alternative Approach Using Built-in Methods

We can also solve this using Python's find() method for a more concise solution ?

def get_min_index_char_optimized(str_input, patt):
    min_index = float('inf')
    min_char = -1
    
    for char in patt:
        index = str_input.find(char)
        if index != -1 and index < min_index:
            min_index = index
            min_char = char
    
    return min_char

# Test the optimized function
str_input = "helloworld"
patt = "wor"
result = get_min_index_char_optimized(str_input, patt)
print(f"Character at minimum index: {result}")

The output of the above code is ?

Character at minimum index: o

Conclusion

Both approaches solve the problem effectively. The first method uses nested loops for explicit searching, while the second uses Python's built-in find() method for cleaner code. Choose the approach that best fits your coding style and requirements.