思路：
之前想直接开左右两边的数结果爆内存...
枚举每次pivot的位置，然后数位DP，如果sum<0返回0，因为已经小于零说明已经到了pivot右边，继续dfs只会越来越小，且dp数组会炸
注意一下一些细节：dp开long long，注意前导零只能算一次
代码：
#include<iostream>
#include<algorithm>
#define ll long long
const int N = 50000+5;
const int INF = 0x3f3f3f3f;
using namespace std;
int dig[20];
ll dp[20][20][2000];
ll dfs(int pos,int piv,int sum,bool limit){if(pos == -1) return sum == 0? 1 : 0;if(sum < 0) return 0;if(!limit && dp[pos][piv][sum] != -1) return dp[pos][piv][sum];int top = limit? dig[pos] : 9;ll ret = 0;for(int i = 0;i <= top;i++){int tot;if(pos > piv){tot = sum + (pos - piv)*i;}else if(pos < piv){tot = sum - (piv - pos)*i;}else{tot = sum;}ret += dfs(pos - 1,piv,tot,limit && i == top);}if(!limit) dp[pos][piv][sum] = ret;return ret;
}
ll solve(ll x){int pos = 0;if(x == -1) return 0;while(x){dig[pos++] = x % 10;x /= 10;}ll ret = 0;for(int i = 0;i < pos;i++){ret += dfs(pos - 1,i,0,true);}return ret - pos + 1; //前导零只能算一次
}
int main(){int T;ll l,r;scanf("%d",&T);while(T--){memset(dp,-1,sizeof(dp));scanf("%lld%lld",&l,&r);printf("%lld\n",solve(r) - solve(l - 1));}return 0;
}
