Q1 Strings: Remove exactly one character to make strings equal

Q1Strings.java

import java.io.*;
import java.lang.*;
import java.util.*;

public class Q1Strings {

    public static boolean equalsWhenOneCharRemoved(String x, String y) {
        // Time complexity: O(N)
        // Space complexity: O(1)
        int diff = 0;
        int m = x.length();
        int n = y.length();

        // x and y should differ by exactly 1 in length.
        // If they do not differ in length by 1, then return false directly.
        if (Math.abs(m - n) != 1) return false;


        if (m < n) {
            // We will iterate over the larger string.
            // To make the first argument larger, we call this function again
            // if the x is smaller in length than y.
            return equalsWhenOneCharRemoved(y, x);
        }

        // If here, it is guaranteed that len(x) - len(y) == 1
        // Iterate over the larger string and compare character by character
        // and count the diffs.
        for (int i = 0; i < x.length(); ++i) {
            char x_ch = x.charAt(i);
            char y_ch = (i < y.length()) ? y.charAt(i) : ' ';
            if (x_ch != y_ch) {
                ++diff;
            }
        }

        if (diff == 1) return true;
        return false;

    }

    public static void main(String args[]) {

        // Couple of test cases:
        assert(equalsWhenOneCharRemoved("x", "y") == false);
        assert(equalsWhenOneCharRemoved("x", "XX") == false);
        assert(equalsWhenOneCharRemoved("yy", "yx") == false);
        assert(equalsWhenOneCharRemoved("abcd", "abxcd") == true);
        assert(equalsWhenOneCharRemoved("xyz", "xz") == true);

        System.out.println("All test cases passed.");
    }
}