CodeForces-1451C.cpp

//
// Created by abdob on 10/29/2022.
//
import java.util.*;
import java.io.*;
import java.awt.*;

public class Main {
public static void main(String[] args) throws Exception {
            InputReader sc = new InputReader(System.in);
            int t=sc.nextInt();
            while(t-->0){
                int n=sc.nextInt(),k=sc.nextInt();
                String a=sc.next(),b=sc.next();
                int[] counta=new int[26];
                int[] countb=new int[26];
                for(int i=0;i<n;i++){
                    counta[a.charAt(i)-'a']++;
                    countb[b.charAt(i)-'a']++;
                }
                boolean z=true;
                for(int i=0;i<26;i++){
                    if(countb[i]>counta[i]){
                        z=false;
                        break;
                    }
                    counta[i]-=countb[i];
                    if(counta[i]%k>0 || (i==25 && counta[i]>0)){
                        z=false;
                        break;
                    }
                    if(i<25)counta[i+1]+=counta[i];
                }
                if(z) System.out.println("YES");
                else System.out.println("NO");
            }
    }
}
class InputReader {
private InputStream stream;
private byte[] buf = new byte[1024];
private int curChar;
private int numChars;
private SpaceCharFilter filter;
private BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
public InputReader(InputStream stream) {
        this.stream = stream;
    }
public int read() {
        if (numChars==-1) throw new InputMismatchException();
        if (curChar >= numChars) {
            curChar = 0;
            try { numChars = stream.read(buf); }
            catch (IOException e) { throw new InputMismatchException(); }

            if(numChars <= 0) return -1;
        }
        return buf[curChar++];
    }
public String nextLine() {
        String str = "";
        try { str = br.readLine(); }
        catch (IOException e) { e.printStackTrace(); }
        return str;
    }
public int nextInt() {
        int c = read();
        while(isSpaceChar(c)) c = read();
        int sgn = 1;
        if (c == '-') {
            sgn = -1;
            c = read();
        }
        int res = 0;
        do {
            if(c<'0'||c>'9') throw new InputMismatchException();
            res *= 10;
            res += c - '0';
            c = read();
        }
        while (!isSpaceChar(c));
        return res * sgn;
    }
public long nextLong() {
        int c = read();
        while (isSpaceChar(c)) c = read();
        int sgn = 1;
        if (c == '-') {
            sgn = -1;
            c = read();
        }
        long res = 0;
        do {
            if (c < '0' || c > '9') throw new InputMismatchException();
            res *= 10;
            res += c - '0';
            c = read();
        }
        while (!isSpaceChar(c));
        return res * sgn;
    }
public double nextDouble() {
        int c = read();
        while (isSpaceChar(c)) c = read();
        int sgn = 1;
        if (c == '-') {
            sgn = -1;
            c = read();
        }
        double res = 0;
        while (!isSpaceChar(c) && c != '.') {
            if (c == 'e' || c == 'E') return res * Math.pow(10, nextInt());
            if (c < '0' || c > '9') throw new InputMismatchException();
            res *= 10;
            res += c - '0';
            c = read();
        }
        if (c == '.') {
            c = read();
            double m = 1;
            while (!isSpaceChar(c)) {
                if (c == 'e' || c == 'E') return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9') throw new InputMismatchException();
                m /= 10;
                res += (c - '0') * m;
                c = read();
            }
        }
        return res * sgn;
    }
public String readString() {
        int c = read();
        while (isSpaceChar(c)) c = read();
        StringBuilder res = new StringBuilder();
        do { res.appendCodePoint(c);c = read();}
        while (!isSpaceChar(c));
        return res.toString();
    }
public boolean isSpaceChar(int c) {
        if (filter != null) return filter.isSpaceChar(c);
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }
public String next() { return readString();}
public interface SpaceCharFilter { public boolean isSpaceChar(int ch);}
}