Problem:
Score : 300 points

Problem Statement

Dolphin resides in two-dimensional Cartesian plane, with the positive x-axis pointing right and the positive y-axis pointing up.

Currently, he is located at the point (sx,sy). In each second, he can move up, down, left or right by a distance of 1.

Here, both the x- and y-coordinates before and after each movement must be integers.

He will first visit the point (tx,ty) where sx < tx and sy < ty, then go back to the point (sx,sy), then visit the point (tx,ty) again, and lastly go back to the point (sx,sy).

Here, during the whole travel, he is not allowed to pass through the same point more than once, except the points (sx,sy) and (tx,ty).

Under this condition, find a shortest path for him.

Constraints

-1000 ≤ sx < tx ≤ 1000

-1000 ≤ sy < ty ≤ 1000

sx,sy,tx and ty are integers.

Input

The input is given from Standard Input in the following format:

sx sy tx ty

Output

Print a string S that represents a shortest path for Dolphin.

The i-th character in S should correspond to his i-th movement.

The directions of the movements should be indicated by the following characters:

U: Up

D: Down

L: Left

R: Right

If there exist multiple shortest paths under the condition, print any of them.

Sample Input 1

0 0 1 2

Sample Output 1

UURDDLLUUURRDRDDDLLU

One possible shortest path is:

Going from (sx,sy) to (tx,ty) for the first time: (0,0) → (0,1) → (0,2) → (1,2)

Going from (tx,ty) to (sx,sy) for the first time: (1,2) → (1,1) → (1,0) → (0,0)

Going from (sx,sy) to (tx,ty) for the second time: (0,0) → (-1,0) → (-1,1) → (-1,2) → (-1,3) → (0,3) → (1,3) → (1,2)

Going from (tx,ty) to (sx,sy) for the second time: (1,2) → (2,2) → (2,1) → (2,0) → (2,-1) → (1,-1) → (0,-1) → (0,0)

Sample Input 2

-2 -2 1 1

Sample Output 2

UURRURRDDDLLDLLULUUURRURRDDDLLDL

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.lang.Character.Subset;
import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.time.temporal.ValueRange;
import java.util.AbstractMap;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Set;
import java.util.Stack;
import java.util.TreeMap;
import java.util.TreeSet;

import static java.util.Comparator.*;

public class Main {

    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        MyInput in = new MyInput(inputStream);
        PrintWriter out = new PrintWriter(outputStream);

        Solver solver = new Solver(in, out);
        solver.solve();

        out.close();
    }

    // ======================================================================
    static class Solver {
    	MyInput in;
    	PrintWriter out;
        public Solver(MyInput in, PrintWriter out) {
        	this.in = in;
        	this.out = out;
        }
        
        // ======================================================================
        public void solve() {
        	int sx = ni();
        	int sy = ni();
        	int tx = ni();
        	int ty = ni();
        	StringBuffer ans = new StringBuffer();
        	for (int i = 0; i < tx - sx; i++) 	ans.append("R");
        	for (int i = 0; i < ty - sy; i++) 	ans.append("U");
        	for (int i = 0; i < tx - sx; i++) 	ans.append("L");
        	for (int i = 0; i < tx - sx; i++) 	ans.append("D");
        	ans.append("D");
        	for (int i = 0; i < tx - sx + 1; i++) 	ans.append("R");
        	for (int i = 0; i < ty - sy + 1; i++) 	ans.append("U");
        	ans.append("L");	ans.append("U");
        	for (int i = 0; i < tx - sx + 1; i++)	ans.append("L");
        	for (int i = 0; i < tx - sx + 1; i++) 	ans.append("D");
        	ans.append("R");
        	prn(ans.toString());
        }
        // -----------------------------------------
        // Integer のキーに対して、カウントを管理する（カウントを足したり、引いたりする）
        static class MapCounter {
        	private Map<Integer, Long> map = new HashMap<>();
        	public MapCounter() {}
        	// キーのカウントに値を足す
        	public void add(int key) {
        		add(key, 1);
        	}
           	public void add(int key, int cnt) {
        		Long val = map.get(key);
        		if(val == null) {
        			map.put(key, (long)cnt);
        		} else {
        			map.put(key,  val + cnt);
        		}
        	}
           	// キーのカウントから値を引く
        	public void sub(int key) {
        		sub(key, 1);
        	}
        	public void sub(int key, int cnt) {
        		Long val = map.get(key);
        		if(val == null) {
        			map.put(key, (long)-cnt);
        		} else {
        			map.put(key,  val - cnt);
        		}
        	}
        	// キーのカウントを取得する（なければ　ＮＵＬＬを返す）
        	public Long getCountwithNull(int key) {
        		return map.get(key);
        	}
        	// キーのカウントを取得する（なければ　０　を返す）
        	public Long getCount(int key) {
        		Long val = map.get(key);
        		if(val == null)		return 0L;
        		else 				return val;
        	}
        	public Set<Integer> getKey() {
        		return map.keySet();
        	}
        	// 登録されているキーの数を返す
        	public int getKeyCount() {
        		return map.keySet().size();
        	}
        }
        // -----------------------------------------
        // 配列のバイナリーサーチ　１
        boolean isRightMin(int[] a, boolean f, int index, int key) {
    	    if (f && a[index] >= key)		return true;		// 以上
    	    else if (!f && a[index] > key)	return true;		// より大きい
    	    else 							return false;	
    	}
    	// 配列 a の中で key 以上（f=true)または、より大きく（f=false)、一番小さい値を返す
    	int binarySearchRightMin(int[] a, boolean f, int key) {	
    	    int ng = -1; 				//「index = 0」が条件を満たすこともあるので、初期値は -1	
    	    int ok = (int)a.length; 	// 「index = a.length-1」が条件を満たさないこともあるので、初期値は a.length()	
    		
    	    /* ok と ng のどちらが大きいかわからないことを考慮 */	
    	    while (Math.abs(ok - ng) > 1) {	
    	        int mid = (ok + ng) / 2;	
    		
    	        if (isRightMin(a, f, mid, key))	ok = mid;	// 下半分を対象とする
    	        else 							ng = mid;	// 上半分を対象とする
    	    }	
    	    return ok;		// ←　ここで返すのは　isOK() が true の時にセットする方（ok / ng)
    	}
        // -----------------------------------------
        // 配列のバイナリーサーチ　２
        boolean isLeftMax(int[] a, boolean f, int index, int key) {
    	    if (f && a[index] <= key)		return true;		// 以下
    	    else if (!f && a[index] < key)	return true;		// より小さい
    	    else 							return false;	
    	}
    	// 配列 a の中で key 以下（f=true)または、より小さい（f=false)、一番大きい値を返す
    	int binarySearchLeftMax(int[] a, boolean f, int key) {	
    	    int ng = -1; 				//「index = 0」が条件を満たすこともあるので、初期値は -1	
    	    int ok = (int)a.length; 	// 「index = a.length-1」が条件を満たさないこともあるので、初期値は a.length()	
    		
    	    /* ok と ng のどちらが大きいかわからないことを考慮 */	
    	    while (Math.abs(ok - ng) > 1) {	
    	        int mid = (ok + ng) / 2;	
    		
    	        if (isLeftMax(a, f, mid, key))	ng = mid;	// 上半分を対象とする
    	        else 							ok = mid;	// 下半分を対象とする
    	    }	
    	    return ng;		// ←　ここで返すのは　isOK() が true の時にセットする方（ok / ng)
    	}
    	
        // -----------------------------------------
    	// オイラーツアー（部分木対応）
    	static class EulerTour {
    		Graph g;
    		List<Integer> euler_tour = new ArrayList<>();
    		int[] begin, end;
    		int k = 0, root = 0;
    		
    		void dfs(int v,int p, PrintWriter out) {
    			out.println("v = " + v + "  p = " + p);
    			begin[v] = k;
    			euler_tour.add(v);
    			k++;
    			if(!g.contains(v)) {
    				return;
    			}
    			for(int i : g.get(v)) {
    				if(i != p) {
    					dfs(i, v, out);
    					euler_tour.add(v);
    					k++;
    				}
    			}
    			end[v]=k;
    		}
    		// 初期化
    		public void init(int p_cnt, int root, Graph g, PrintWriter out) {
    			begin = new int[p_cnt + 1];
    			end = new int[p_cnt + 1];
    			this.root = root;
    			this.g = g;
    			dfs(root, -1, out);
    		}
    		// 部分木の頂点を渡すと、オイラーツアーの部分木を返す
    		public List getPartTour(int v) {
    			return euler_tour.subList(begin[v], end[v]);
    		}
    		// 部分木の頂点を渡すと、頂点のリストを返す
    		public List<Integer> getPartList(int v) {
    			Set<Integer> set = new TreeSet<>();
				set.addAll(getPartTour(v));
				List<Integer> ans = new ArrayList<>();
				for(Integer p : set) {
					ans.add(p);
				}
				return ans;
    		}
    	}
    	
        // -----------------------------------------
        // グラフのリンクリスト
        static class Graph {
        	// 頂点に紐づく頂点のリスト
            private Map<Integer, List<Integer>> data = new HashMap<Integer, List<Integer>>();
//            // 全ての頂点のセット
//            private Set<Integer> point = new TreeSet<>();
            // 頂点と頂点の繋がりを追加する
            void add(int from, int to) {
            	List<Integer> list = data.get(from);
            	if(list == null) {
            		list = new ArrayList<Integer>();
            		data.put(from, list);
            	}
            	list.add(to);
//            	point.add(key);
//            	point.add(value);
            }
            // 指定された頂点に紐づく、頂点のリストを返す
            List<Integer> get(int key) {
            	return data.get(key);
            }
            // 頂点 key が登録されているか？
            boolean contains(int key) {
            	return data.containsKey(key);
            }
            
            //　頂点のセットを返す
            Set<Integer> keySet() {
            	return data.keySet();
            }
            // 頂点　key_1 と 頂点　key_2 がつながっていれば　true を返す
            boolean isConnect(int key_1, int key_2) {
            	List<Integer> list = data.get(key_1);
            	if(list == null)	return false;
            	else 				return list.contains(key_2);
            }
            // 指定された頂点から、すべての頂点への距離を返す
            List<PP> distList(int key) {
            	List<PP> dist = new ArrayList<>();		// 頂点と距離のペアのリスト
            	Set<Integer> mark = new HashSet<>();	// 処理したら入れる
    			Stack<PP> stack = new Stack<>();		// スタックの宣言
    			stack.push(new PP(key, 0));				// スタートをスタックに保存
    			while(!stack.isEmpty()) {
    				PP wk = stack.pop();				// スタックから次の頂点を取得
    				int pp = wk.getKey();
    				int dd = wk.getVal();
    				mark.add(pp);						// 通過マーク
        			dist.add(new PP(pp, dd));			// 距離を登録
    				List<Integer> list = get(pp);		// つながっている頂点のリストを取得
    				for(int next : list) {
    					if(mark.contains(next))	continue;
    					stack.push(new PP(next, dd + 1));
    				}
    			}
    			return dist;
            }
            // ダンプ
            void dump(PrintWriter out) {
            	for(int key : data.keySet()) {
            		out.print(key + " : ");
            		for(int val : data.get(key)) {
            			out.print(val + " ");
            		}
            		out.println("");
            	}
            }
        }
        // -----------------------------------------
        // 重さを持ったグラフのリンクリスト
        static class GraphWith {
        	// キーに紐づくリストに、頂点番号と重さのペアを持つ
            private Map<Integer, List<PP>> data = new HashMap<Integer, List<PP>>();
            // 指定された頂点に紐づく、頂点と重さのペアを追加する
            void add(int key, PP p) {
            	List<PP> list = data.get(key);
            	if(list == null) {
            		list = new ArrayList<PP>();
            		data.put(key, list);
            	}
            	list.add(p);
            }
            // 頂点に紐づく、頂点と重さのペアのリストを返す
            List<PP> get(int key) {
            	return data.get(key);
            }
            // グラフの存在チェック（重さは関係しない）
            // 頂点　key と 頂点　value がつながっていれば　true を返す
            boolean contains(int key, int value) {
            	List<PP> list = data.get(key);
            	if(list == null)	return false;
            	boolean ans = false;
            	for(PP p : list) {
            		if(p.getKey() == value) {
            			ans = true;
            			break;
            		}
            	}
            	return ans;
            }
        }
        // -----------------------------------------
        // グラフのリンクリスト(Long)
        static class GraphLong {
            private Map<Long, List<Long>> G = new HashMap<Long, List<Long>>();
            void add(long key, long value) {
            	List<Long> list = G.get(key);
            	if(list == null) {
            		list = new ArrayList<Long>();
            		G.put(key, list);
            	}
            	list.add(value);
            }
            List<Long> get(long key) {
            	return G.get(key);
            }
        }
        // -----------------------------------------
        // 重さを持ったグラフのリンクリスト(Long)
        static class GraphLongWith {
            private Map<Long, List<PPL>> G = new HashMap<Long, List<PPL>>();
            void add(long key, PPL p) {
            	List<PPL> list = G.get(key);
            	if(list == null) {
            		list = new ArrayList<PPL>();
            		G.put(key, list);
            	}
            	list.add(p);
            }
            List<PPL> get(long key) {
            	return G.get(key);
            }
        }
        // -----------------------------------------

        void prn(String s) {
        	out.println(s);
        }
        void prn(int i) {
        	out.println(i);
        }
        void prn(long i) {
        	out.println(i);
        }
        void prr(String s) {
        	out.print(s);
        }
        int ni() {
        	return in.nextInt();
        }
        long nl() {
        	return in.nextLong();
        }
        double nd() {
        	return in.nextDouble();
        }
        String ns() {
        	return in.nextString();
        }
        int[] ndi(int n) {
        	int[] ans = new int[n];
        	for(int i=0; i < n; i++) {
        		ans[i] = ni();
        	}
        	return ans;
        }
        long[] ndl(int n) {
        	long[] ans = new long[n];
        	for(int i=0; i < n; i++) {
        		ans[i] = nl();
        	}
        	return ans;
        }
        double[] ndd(int n) {
        	double[] ans = new double[n];
        	for(int i=0; i < n; i++) {
        		ans[i] = nd();
        	}
        	return ans;
        }
        String[] nds(int n) {
        	String[] ans = new String[n];
        	for(int i=0; i < n; i++) {
        		ans[i] = ns();
        	}
        	return ans;
        }
        int[][] nddi(int n, int m) {
        	int[][] ans = new int[n][m];
        	for(int i=0; i < n; i++) {
            	for(int j=0; j < m; j++) {
            		ans[i][j] = ni();
            	}
        	}
        	return ans;
        }
        long[][] nddl(int n, int m) {
        	long[][] ans = new long[n][m];
        	for(int i=0; i < n; i++) {
            	for(int j=0; j < m; j++) {
            		ans[i][j] = nl();
            	}
        	}
        	return ans;
        }
    }
    static class PP{
    	public int key, val;
    	public PP(int key, int val) {
    		this.key = key;
    		this.val = val;
    	}
		public int getKey() {
			return key;
		}
		public void setKey(int key) {
			this.key = key;
		}
		public int getVal() {
			return val;
		}
		public void setVal(int val) {
			this.val = val;
		}
    }
    static class PPL {
    	public long key, val;
    	public PPL(long key, long val) {
    		this.key = key;
    		this.val = val;
    	}
		public long getKey() {
			return key;
		}
		public void setKey(long key) {
			this.key = key;
		}
		public long getVal() {
			return val;
		}
		public void setVal(long val) {
			this.val = val;
		}
    }
    static class PPDL {
    	public long key;
    	public long[] val;
    	public PPDL(long key, long[] val) {
    		this.key = key;
    		this.val = val;
    	}
		public long getKey() {
			return key;
		}
		public void setKey(long key) {
			this.key = key;
		}
		public long[] getVal() {
			return val;
		}
		public void setVal(long[] val) {
			this.val = val;
		}
		public void dump(PrintWriter out) {
			out.print("key = " + key + "  val ");
			for(int i=0; i < val.length; i++) {
				out.print("[" + val[i] + "] ");
			}
			out.println("");
		}
    }
    // HashMap のキーに使う
    static final class PPKEY{
    	private final int key, val;
    	public PPKEY(int key, int val) {
    		this.key = key;
    		this.val = val;
    	}
		public int getKey() {
			return key;
		}
		public int getVal() {
			return val;
		}
	    @Override
	    public boolean equals(Object obj) {
	        if (obj instanceof PPKEY) {
	        	PPKEY dest = (PPKEY) obj;
	            return this.key == dest.key && this.val == dest.val;
	        } else {
	            return false;
	        }
	    }
	    @Override
	    public int hashCode() {
	        return Objects.hash(key, val);
	    }
    }
    // HashMap のキーに使う
    static final class PPLKEY{
    	private final long key, val;
    	public PPLKEY(long key, long val) {
    		this.key = key;
    		this.val = val;
    	}
		public long getKey() {
			return key;
		}
		public long getVal() {
			return val;
		}
	    @Override
	    public boolean equals(Object obj) {
	        if (obj instanceof PPKEY) {
	        	PPKEY dest = (PPKEY) obj;
	            return this.key == dest.key && this.val == dest.val;
	        } else {
	            return false;
	        }
	    }
	    @Override
	    public int hashCode() {
	        return Objects.hash(key, val);
	    }
    }
    // ======================================================================
    static class Pair<K, V> extends AbstractMap.SimpleEntry<K, V> {
        /** serialVersionUID. */
        private static final long serialVersionUID = 6411527075103472113L;

        public Pair(final K key, final V value) {
            super(key, value);
        }
     }
    static class MyInput {
        private final BufferedReader in;
        private static int pos;
        private static int readLen;
        private static final char[] buffer = new char[1024 * 8];
        private static char[] str = new char[500 * 8 * 2];
        private static boolean[] isDigit = new boolean[256];
        private static boolean[] isSpace = new boolean[256];
        private static boolean[] isLineSep = new boolean[256];

        static {
            for (int i = 0; i < 10; i++) {
                isDigit['0' + i] = true;
            }
            isDigit['-'] = true;
            isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true;
            isLineSep['\r'] = isLineSep['\n'] = true;
        }

        public MyInput(InputStream is) {
            in = new BufferedReader(new InputStreamReader(is));
        }

        public int read() {
            if (pos >= readLen) {
                pos = 0;
                try {
                    readLen = in.read(buffer);
                } catch (IOException e) {
                    throw new RuntimeException();
                }
                if (readLen <= 0) {
                    throw new MyInput.EndOfFileRuntimeException();
                }
            }
            return buffer[pos++];
        }

        public int nextInt() {
            int len = 0;
            str[len++] = nextChar();
            len = reads(len, isSpace);
            int i = 0;
            int ret = 0;
            if (str[0] == '-') {
                i = 1;
            }
            for (; i < len; i++) ret = ret * 10 + str[i] - '0';
            if (str[0] == '-') {
                ret = -ret;
            }
            return ret;
        }

        public long nextLong() {
            int len = 0;
            str[len++] = nextChar();
            len = reads(len, isSpace);
            int i = 0;
            long ret = 0L;
            if (str[0] == '-') {
                i = 1;
            }
            for (; i < len; i++) ret = ret * 10 + str[i] - '0';
            if (str[0] == '-') {
                ret = -ret;
            }
            return ret;
        }

        public double nextDouble() {
            int len = 0;
            str[len++] = nextChar();
            len = reads(len, isSpace);
            int i = 0;
            double ret = 0;
            if (str[0] == '-') {
                i = 1;
            }
            int cnt = 0;
            for (; i < len; i++) {
            	if(str[i] == '.') {
            		cnt = 10;
            		continue;
            	}
            	if(cnt == 0) {
            		ret = ret * 10 + str[i] - '0';
            	} else {
            		ret = ret + ((double)(str[i] - '0') / cnt);
            		cnt *= 10;
            	}
            }
            if (str[0] == '-') {
                ret = -ret;
            }
            return ret;
        }

       public String nextString() {
        	String ret = new String(nextDChar()).trim();
            return ret;
        }

        public char[] nextDChar() {
            int len = 0;
            len = reads(len, isSpace);
            char[] ret = new char[len + 1];
            for (int i=0; i < len; i++)		ret[i] = str[i];
            ret[len] = 0x00;
            return ret;
        }

        public char nextChar() {
            while (true) {
                final int c = read();
                if (!isSpace[c]) {
                    return (char) c;
                }
            }
        }

        int reads(int len, boolean[] accept) {
            try {
                while (true) {
                    final int c = read();
                    if (accept[c]) {
                        break;
                    }
                    if (str.length == len) {
                        char[] rep = new char[str.length * 3 / 2];
                        System.arraycopy(str, 0, rep, 0, str.length);
                        str = rep;
                    }
                    str[len++] = (char) c;
                }
            } catch (MyInput.EndOfFileRuntimeException e) {
            }
            return len;
        }

        static class EndOfFileRuntimeException extends RuntimeException {
        }
    }
}