hdu 3183 A Magic Lamp(模拟解法)

思路见代码，递归写法很容易懂。

证明：反证。

/*
author:ray007great
version:1.0
*/
#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<vector>
#include<set>
#include<map>
#include<string>
#include<time.h>
#include<queue>
using namespace std;
typedef long long ll;
//c++
#pragma comment(linker, "/STACK:102400000,102400000")
// g++
//int size = 256 << 20; // 256MB
//char *p = (char*)malloc(size) + size;
//__asm__("movl %0, %esp\n" :: "r"(p) );

#define sf(a) scanf("%d",&a)
#define sfs(a) scanf("%s",a)
#define sfI(a) scanf("%I64d",&a)
#define pf(a) printf("%d\n",a)
#define pfI(a) printf("%I64d\n",a)
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define repd(i,a,b) for(int i=(a);i>=(b);i--)
#define rep1(i,a,b) for(int i=(a);i<(b);i++)
#define clr(a) memset(a,0,sizeof(a))
#define clr1(a) memset(a,-1,sizeof(a))
#define pfk printf("fuck\n")

/* define */

/* clock */

//clock_t start, finish;
//start = clock();
//finish = clock();
//double duration = (double)(finish - start)/CLOCKS_PER_SEC;
//printf( "%.10f seconds\n", duration );

/* clock */

/* data */
/* data */
string str,ans,res1,res2;
int k;
void del1(int l,int r);
void del2(int l,int r);
void del2(int l,int r){
if(k==0||res2=="") return;
for(int i=l;i<r;i++){
if(res2[i]>res2[i+1]){
res1="";
for(int j=l;j<=r;j++){
if(j==i) continue;
res1+=res2[j];
}
k--;
del1(0,r-1);
return ;
}
}
return ;
}
void del1(int l,int r){
if(k==0||res1=="") return ;
for(int i=l;i<r;i++){
if(res1[i]>res1[i+1]){
res2="";
for(int j=l;j<=r;j++){
if(j==i) continue;
res2+=res1[j];
}
k--;
del2(0,r-1);
return ;
}
}
return ;
}
bool isDel[2500];
int main(){
while(cin>>str){
cin>>k;
res1="";res2="";
for(int i=0;str[i];i++) res1+=str[i];
ans="";
del1(0,str.length()-1);
int len1=res1.length();
int len2=res2.length();
if(len1<=len2||(len1&&!len2)){
for(int i=0;i<len1;i++)
ans+=res1[i];
}
else {
for(int i=0;i<len2;i++)
ans+=res2[i];
}
int len=ans.length();
clr(isDel);
for(int i=len-1;i>=0;i--){
if(k==0) break;
isDel[i]=true;
k--;
}
int flag=0;
for(int i=0;ans[i];i++){
if(isDel[i]) continue;
if(ans[i]=='0'&&!flag) continue;
flag=1;
cout<<ans[i];
}
if(!flag) cout<<0;
cout<<endl;
}
return 0;
}