C++解答

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <algorithm>
using namespace std;

typedef long long ll;

ll dp[20][20][20][20];
ll l,r;
int num[20],len;


inline ll dfs(int i,int s,int p,int q,bool e,bool pre){
    if(i==-1){
        if(s<=1) return 1;
        return 0;
    }
    if(!e && dp[i][s][p][q]!=-1) return dp[i][s][p][q];
    int v=(e?num[i]:9);
    ll ans=0;
    for(int j=0;j<=v;j++){
        int news=s;
        if(j!=4&&j!=7){
            if(j!=0||(!pre&&j==0))
                news++;
        }
        ans+=dfs(i-1,news,p+(j==4),q+(j==7),e&&(j==v),(j==0&&pre));
    }
    if(!e) dp[i][s][p][q]=ans;
    return ans;
}
inline ll solve(ll n){
    if(n<0) return 0;
    if(n==0) return 1;
    len=0;
    while(n){
        num[len++]=n%10;
        n/=10;
    }
    //for(int i=0;i<len;i++) printf("%d z\n",num[i]);
    return dfs(len-1,0,0,0,1,1);
}

int gao(ll w){
    int a=0;
    while(w){
        int b=w%10;
        w/=10;
        if(b!=4&&b!=7) a++;
    }
    return a;
}
int main(){

    memset(dp,-1,sizeof(dp));
    int ans=0;
   // printf("%d z\n",ans);
    while(~scanf("%lld%lld",&l,&r)){
            printf("%lld\n",solve(r)-solve(l-1));
    }
    return 0;
}

Java解答

import java.io.*;
import java.math.*;
import java.util.*;

public class Main {
	static long a, b, tmp;
	static int cnt;

	static void dfs(long n, boolean has) {
		if (n > a)
			return;
		if (n >= b && n <= a)
			cnt++;
		dfs(n * 10 + 4, has);
		dfs(n * 10 + 7, has);
		if (has)
			for (int i = (n == 0 ? 1 : 0); i <= 9; i++) {
				if (i == 4 || i == 7)
					continue;
				dfs(n * 10 + i, false);
			}
	}

	public static void main(String[] args) {
		InputReader cin = new InputReader(System.in);
		OutputWriter out = new OutputWriter(System.out);
		while (cin.hasNext()) {
			a = cin.nextLong();
			b = cin.nextLong();
			if (a < b) {
				tmp = a;
				a = b;
				b = tmp;
			}
			cnt = 0;
			dfs(0, true);
			out.println(cnt);
		}
      	out.close();
	}
}

class InputReader {
	private boolean finished = false;

	private InputStream stream;
	private byte[] buf = new byte[1024];
	private int curChar;
	private int numChars;
	private SpaceCharFilter filter;

	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 int peek() {
		if (numChars == -1)
			return -1;
		if (curChar >= numChars) {
			curChar = 0;
			try {
				numChars = stream.read(buf);
			} catch (IOException e) {
				return -1;
			}
			if (numChars <= 0)
				return -1;
		}
		return buf[curChar];
	}

	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 String nextString() {
		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 isWhitespace(c);
	}

	public static boolean isWhitespace(int c) {
		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
	}

	private String readLine0() {
		StringBuilder buf = new StringBuilder();
		int c = read();
		while (c != '\n' && c != -1) {
			if (c != '\r')
				buf.appendCodePoint(c);
			c = read();
		}
		return buf.toString();
	}

	public String nextLine() {
		String s = readLine0();
		while (s.trim().length() == 0)
			s = readLine0();
		return s;
	}

	public String nextLine(boolean ignoreEmptyLines) {
		if (ignoreEmptyLines)
			return nextLine();
		else
			return readLine0();
	}

	public BigInteger nextBigInteger() {
		try {
			return new BigInteger(nextString());
		} catch (NumberFormatException e) {
			throw new InputMismatchException();
		}
	}

	public char nextCharacter() {
		int c = read();
		while (isSpaceChar(c))
			c = read();
		return (char) c;
	}

	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 boolean isExhausted() {
		int value;
		while (isSpaceChar(value = peek()) && value != -1)
			read();
		return value == -1;
	}

	public boolean hasNext() {
		return !isExhausted();
	}

	public String next() {
		return nextString();
	}

	public SpaceCharFilter getFilter() {
		return filter;
	}

	public void setFilter(SpaceCharFilter filter) {
		this.filter = filter;
	}

	public interface SpaceCharFilter {
		public boolean isSpaceChar(int ch);
	}
}

class OutputWriter {
	private final PrintWriter writer;

	public OutputWriter(OutputStream outputStream) {
		writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(
				outputStream)));
	}

	public OutputWriter(Writer writer) {
		this.writer = new PrintWriter(writer);
	}

	public void print(Object... objects) {
		for (int i = 0; i < objects.length; i++) {
			if (i != 0)
				writer.print(' ');
			writer.print(objects[i]);
		}
	}

	public void print(int[] array) {
		for (int i = 0; i < array.length; i++) {
			if (i != 0)
				writer.print(' ');
			writer.print(array[i]);
		}
	}

	public void print(long[] array) {
		for (int i = 0; i < array.length; i++) {
			if (i != 0)
				writer.print(' ');
			writer.print(array[i]);
		}
	}

	public void printLine(int[] array) {
		print(array);
		writer.println();
	}

	public void printLine(long[] array) {
		print(array);
		writer.println();
	}

	public void printLine() {
		writer.println();
	}

	public void printLine(Object... objects) {
		print(objects);
		writer.println();
	}

	public void print(char i) {
		writer.print(i);
	}

	public void printLine(char[] array) {
		writer.println(array);
	}

	public void printFormat(String format, Object... objects) {
		writer.printf(format, objects);
	}

	public void println(Object... objects) {
		print(objects);
		writer.println();
	}

	public void println() {
		writer.println();
	}

	public void printf(String format, Object... args) {
		writer.printf(format, args);
	}

	public void close() {
		writer.close();
	}

	public void flush() {
		writer.flush();
	}
}