瑶瑶的第K大 ACdream-1099

题目：https://vjudge.net/problem/ACdream-1099

分析

因为是中文版所以说的已经很详细了。就是n很多k很大需要注意，提供一个输入外挂函数scan_d，然后二分节省时间。

代码

/******************************************************************** * File Name: kth_big_number.cpp * Author: Sequin * mail: [e-mail] * Created Time: 四  8/ 3 15:06:51 2017 *************************************************************************/#include <iostream>#include <stdio.h>#include <string.h>#include <stack>#include <queue>#include <map>#include <ctype.h>#include <set>#include <vector>#include <cmath>#include <bitset>#include <algorithm>#include <climits>#include <string>#include <list>#include <cctype>#include <cstdlib>#include <fstream>#include <sstream>using namespace std;#define lson 2*i#define rson 2*i+1#define LS l,mid,lson#define RS mid+1,r,rson#define UP(i,x,y) for(i=x;i<=y;i++)#define DOWN(i,x,y) for(i=x;i>=y;i--)#define MEM(a,x) memset(a,x,sizeof(a))#define W(a) while(a)#define gcd(a,b) __gcd(a,b)#define pi acos(-1.0)#define pii pair<int,int>#define ll long long#define MAX 1000005#define MOD 1000000007#define INF 0x3F3F3F3F#define EXP 1e-8#define lowbit(x) (x&-x)ll qpow(ll p,ll q){ll f=1;while(q){if(q&1)f=f*p;p=p*p;q>>=1;}return f;}int n, k;int count = 0;int a[6000000];inline bool scan_d(int &ret){    char c; int sgn;    if (c = getchar(), c ==EOF) return 0;    while (c != '-' && (c <'0' || c > '9')) c = getchar();    sgn = (c == '-') ? -1 : 1;    ret = (c == '-') ? 0 : (c - '0');    while (c = getchar() , (c >= '0' && c <= '9'))        ret = ret * 10  + (c - '0');    ret *= sgn;    return 1;}inline int findk(int l, int r, int k){    if(l == r){        return a[l];    }    int ll = l, rr = r;    int kk = a[l];    while(ll < rr){        while(a[rr] <= kk && ll < rr)            rr--;        if(ll < rr)            a[ll++] = a[rr];        while(a[ll] >= kk && ll < rr)            ll++;        if(ll < rr){            a[rr--] = a[ll];        }    }    a[ll] = kk;    if(ll > k){        return findk(l, ll-1, k);    }    else if(ll < k){        return findk(ll+1, r, k);    }else{        return a[ll];    }}int main(){    scanf("%d%d", &n, &k);    {        getchar();        for (int i = 1; i <= n; i++)        {            scan_d(a[i]);        }        int ret = findk(1, n, k);        printf("%d\n", ret);    }    return 0;}