description: You are given two integers n and m. Find the \operatorname{MEX} of the sequence n ⊕ 0, n ⊕ 1, …, n ⊕ m. Here, ⊕ is the [bitwise XOR operator](https://en.wikipedia.org/wiki/Bitwise_operation#XOR).
  
  \operatorname{MEX} of the sequence of non-negative integers is the smallest non-negative integer that doesn't appear in this sequence. For example, \operatorname{MEX}(0, 1, 2, 4) = 3, and \operatorname{MEX}(1, 2021) = 0. 
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 30 000) — the number of test cases.
  
  The first and only line of each test case contains two integers n and m (0 ≤ n, m ≤ 10^9).
  
  Output
  
  For each test case, print a single integer — the answer to the problem.
  
  Example
  
  Input
  
  
  5
  3 5
  4 6
  3 2
  69 696
  123456 654321
  
  
  Output
  
  
  4
  3
  0
  640
  530866
  
  Note
  
  In the first test case, the sequence is 3 ⊕ 0, 3 ⊕ 1, 3 ⊕ 2, 3 ⊕ 3, 3 ⊕ 4, 3 ⊕ 5, or 3, 2, 1, 0, 7, 6. The smallest non-negative integer which isn't present in the sequence i. e. the \operatorname{MEX} of the sequence is 4.
  
  In the second test case, the sequence is 4 ⊕ 0, 4 ⊕ 1, 4 ⊕ 2, 4 ⊕ 3, 4 ⊕ 4, 4 ⊕ 5, 4 ⊕ 6, or 4, 5, 6, 7, 0, 1, 2. The smallest non-negative integer which isn't present in the sequence i. e. the \operatorname{MEX} of the sequence is 3.
  
  In the third test case, the sequence is 3 ⊕ 0, 3 ⊕ 1, 3 ⊕ 2, or 3, 2, 1. The smallest non-negative integer which isn't present in the sequence i. e. the \operatorname{MEX} of the sequence is 0.
solution: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Random;
  import java.util.StringTokenizer;
  
  public class C {
  
  	public static void main(String[] args) {
  		FastScanner fs=new FastScanner();
  		int T=fs.nextInt();
  		Random r=new Random(5);
  		for (int tt=0; tt<T; tt++) {
  			int n=fs.nextInt(), m=fs.nextInt();
  //			int ans=solve(0, 30, n, m);
  //			int n=r.nextInt(1000), m=r.nextInt(1000);
  			int ans=solve(0, 30, n, m);
  //			if (ans!=solveBF(n, m)) throw null;
  //			System.out.println(solveBF(n, m));
  			System.out.println(ans);
  		}
  	}
  	
  	// assume that there is some element in 
  	// [minAns, minAns+1<<bit) that we don't hit
  	static int solve(int minAns, int bit, int n, int m) {
  		if (bit==-1) return minAns;
  		if (bit<4) {
  //			System.out.println("At: "+minAns+" "+bit);
  		}
  		if ((n&(1<<bit))==0) {
  			//n doesn't have this bit
  			//don't add bit comes first
  			//check if m has everything where this is a 0
  			if (m-minAns>=(1<<bit)-1) {
  				//we hit everything in this range
  				return solve(minAns+(1<<bit), bit-1, n, m);
  			}
  			else {
  				return solve(minAns, bit-1, n, m);
  			}
  			
  		}
  		else {
  			//adding bit comes first
  			//check if m has everything where this is a 0
  //			if (m>=minAns+(1<<bit)-1) {
  //				solve(minAns+(1<<bit), bit+1, n, m);
  //			}
  //			else {
  				return solve(minAns, bit-1, n, m-(1<<bit));
  //			}
  		}
  	}
  	
  	static int solveBF(int n, int m) {
  		boolean[] res=new boolean[1_000_000];
  		for (int i=0; i<=m; i++) {
  			res[n^i]=true;
  		}
  		for (int i=0; true; i++) if (!res[i]) return i;
  	}
  
  	static void sort(int[] a) {
  		ArrayList<Integer> l=new ArrayList<>();
  		for (int i:a) l.add(i);
  		Collections.sort(l);
  		for (int i=0; i<a.length; i++) a[i]=l.get(i);
  	}
  	
  	static class FastScanner {
  		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  		StringTokenizer st=new StringTokenizer("");
  		String next() {
  			while (!st.hasMoreTokens())
  				try {
  					st=new StringTokenizer(br.readLine());
  				} catch (IOException e) {
  					e.printStackTrace();
  				}
  			return st.nextToken();
  		}
  		
  		int nextInt() {
  			return Integer.parseInt(next());
  		}
  		int[] readArray(int n) {
  			int[] a=new int[n];
  			for (int i=0; i<n; i++) a[i]=nextInt();
  			return a;
  		}
  		long nextLong() {
  			return Long.parseLong(next());
  		}
  	}
  
  	
  }
  