弱校联萌 BNU I. Increasing or Decreasing

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【题意】求L，R区间里面严格递增或者严格递减的数的个数。

【解题方法】数位DP。正解给了两种方法，我直接用数位DP水过去了。

【代码君】

////Created by just_sort 2016/10/6//Copyright (c) 2016 just_sort.All Rights Reserved//#include <set>#include <map>#include <queue>#include <stack>#include <cmath>#include <cstdio>#include <cstdlib>#include <cstring>#include <iostream>#include <algorithm>using namespace std;typedef long long LL;int digit[20];LL dp[20][20][5];LL dfs(int l,int pre,int flag,bool jud){    if(l == 0) return 1;    if(!jud && dp[l][pre][flag]!=-1) return dp[l][pre][flag];    int nex = jud?digit[l]:9;    LL ret = 0;    for(int i = 0; i <= nex; i++){        int news;        if(flag==1&&i==0) news = 1;        else if(flag==1||(flag==2&&pre==i)) news = 2;        else if(flag==2) news = pre>i?3:4;        else{            if(flag==3&&i>pre) continue;            if(flag==4&&i<pre) continue;            else news = flag;        }        ret += dfs(l-1,i,news,jud&&(i==nex));    }    if(!jud) dp[l][pre][flag]=ret;    return ret;}LL f(LL num){    int pos = 0;    while(num){        digit[++pos] = num%10;        num /= 10;    }    return dfs(pos,0,1,1);}int main(){    memset(dp,-1,sizeof(dp));    int T;    scanf("%d",&T);    while(T--)    {        LL l,r;        scanf("%lld%lld",&l,&r);        printf("%lld\n",f(r)-f(l-1));    }    return 0;}

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