[AtCoder2165]Median Pyramid Hard 二分答案

来源：互联网发布：sql.executequery 编辑：程序博客网时间：2024/06/07 05:37

套路题
二分答案，然后把大于等于它的变成1小于等于它的变成0
这样子的中位数是很有规律的
找到最上面那个玩意儿是啥就行了

#include <iostream>#include <cstdio>#define N 1000050#define INF (1<<30)#define gc() getchar()using namespace std;int a[N],b[N],n;inline int rd() {    int x=0,f=1; char ch=gc();    while (ch<'0'||ch>'9') ch=='-'?f*=-1:0,ch=gc();    while (ch>='0'&&ch<='9') x=x*10+ch-'0',ch=gc();    return x*f;}int go(int x) {    for (int i=1;i<=2*n-1;i++) b[i] = a[i] >= x;    int p = n % 2 == 0 , cur = INF;    int ret = b[n] ^ p;    for (int i=n-1;i>=1;i--) {        if (b[i] == b[i+1] && n-i < cur) {            cur = n-i;            ret = b[i];        }     }    for (int i=n+1;i<=2*n-1;i++) {        if (b[i] == b[i-1] && i-n < cur) {            cur = i-n;            ret = b[i];        }    }    return ret;}int main() {    n = rd();    for (int i=1;i<=2*n-1;i++) a[i] = rd();    int l = 1 , r = 2 * n - 1;    while (l < r) {        int mid = (l + r + 1) >> 1;        if (go(mid)) l = mid; else r = mid - 1;    }    printf("%d\n",l);    return 0;}

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