解題思路

在這個二插搜索樹中尋找，4和7數量相等，并且大于n的最小數。

相關代碼

import java.util.*;public class Main {static String s;static List<Integer> res = new ArrayList<>();static long n;static long ans=Long.MAX_VALUE;public static void main(String[] args){Scanner scanner = new Scanner(System.in);n = scanner.nextInt();dfs(0,0,0);System.out.print(ans);scanner.close();}public static void dfs(long num,long s4,long s7){if(num>=n&&s4==s7){ans=Math.min(ans,num);return;}if(num>=1000000000){return;}dfs(num*10+4,s4+1,s7);dfs(num*10+7,s4,s7+1);}
}