BestR #31

hdu 5178

求|a[i] - a[j]| <= k (i < j) <i,j>的对数，一开始认为数据不大就直接ans++了，后来结果出来才知道，啊啊啊，too young too simple。总之一个教训

思路：先排序，然后用二分查找寻找a[i] + k 在数组中的位置，然后 ans相加

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <cstdlib>
#include <stack>
#include <cctype>
#include <string>
#include <malloc.h>
#include <queue>
#include <map>

using namespace std;

const int INF = 0xffffff;
const double esp = 10e-;
const double Pi =  * atan(1.0);
const int maxn = +;
const long long mod =  ;
const int dr[] = {,,-,,-,,-,};
const int dc[] = {,,,-,,-,-,};
typedef long long LL;

LL gac(LL a,LL b){
    return b?gac(b,a%b):a;
}

long long a[maxn];

int main()
{
#ifndef ONLINE_JUDGE
    freopen("inpt.txt","r",stdin);
   // freopen("output.txt","w",stdout);
#endif
    int t;
    int n,k;
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&n,&k);
        memset(a,,sizeof(a));
        for(int i = ;i < n;i++){
            scanf("%I64d",&a[i]);
        }
        sort(a,a+n);
        long long ans = ;
        for(int i = ;i < n-;i++){
            long long tmp = a[i] + k;
            int m = upper_bound(a,a+n,tmp)- a;
            ans += (m-i-);
        }
        printf("%I64d\n",ans);
    }
    return ;
}

hdu 5179

题意是：一个数如果其低位小于等于高位，并且高位是相邻地位的整数倍则称为魅力的数，要求求出[L,R]范围内美丽数的个数

思路，dfs暴力。

做到了第二题啦~~

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <cstdlib>
#include <stack>
#include <cctype>
#include <string>
#include <malloc.h>
#include <queue>
#include <map>

using namespace std;

const int INF = 0xffffff;
const double esp = 10e-;
const double Pi =  * atan(1.0);
const int maxn = +;
const long long mod =  ;
const int dr[] = {,,-,,-,,-,};
const int dc[] = {,,,-,,-,-,};
typedef long long LL;

LL gac(LL a,LL b){
    return b?gac(b,a%b):a;
}

int L,R;
int a[],b[];
int arr[];
int cnt;

long long get_num(int x){
    long long tmp = ;
    for(int i = x-;i > ;i--){
        tmp = tmp *  + arr[i];
    }
   // cout << tmp << endl;
    return tmp;
}

void dfs(int x){
    long long tt = get_num(x);
    if(tt > R)
        return;
    if(tt >= L)
        cnt++;
    for(int i = ;i < ;i++){
        int tmp = arr[x-] * i;
        if(tmp < ){
            arr[x] = tmp;
            dfs(x+);
        }
        arr[x] = ;
    }
}

int main()
{
#ifndef ONLINE_JUDGE
    freopen("inpt.txt","r",stdin);
#endif
    int t;
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&L,&R);
        memset(arr,,sizeof(arr));
        cnt = ;
        arr[] = ;
        dfs();
        printf("%d\n",cnt);
    }
    return ;
}

第三题什么的就没做出来……