Ural_1306. Sequence Median(堆)

　　开始直接暴力，然后果断挂掉。T_T...后来看到DIcuss里有人说用Binary heap。然后就在想怎么用堆优化，想了半天没想到。然后看大牛的思路。鹈鹄灌顶啊！！！

思路：先存数列长度的一半+1，然后建立小顶堆。然后输入剩下的元素，如果输入的元素大于堆顶元素，则把堆顶替换掉。再调整一次堆。

My Code：

 

#include <iostream>
#include <cstdio>
#include <algorithm>

using namespace std;

const int N = 125005;

int heap[N];

void heap_adjust(int p, int len) {
    int i, j, tmp;
    i = p; j = i << 1;
    tmp = heap[p];
    while(j <= len) {
        if(j < len && heap[j] > heap[j+1])    j++;
        if(tmp > heap[j]) {
            heap[i] = heap[j];
            i = j; j = i << 1;
        }
        else     break;
    }
    heap[i] = tmp;
}

int main() {
    //freopen("data.in", "r", stdin);

    int h, n, i, t;

    while(~scanf("%d", &n)){
    h = n/2 + 1;

    for(i = 1; i <= h; i++)
        scanf("%d", &heap[i]);
    for(i = h/2; i > 0; i--)
        heap_adjust(i, h);

    if(n == 2) {
        printf("%.1lf\n", (heap[1]*1.0 + heap[2]*1.0)/2);
        return 0;
    }

    for(i = h+1; i <= n; i++) {
        scanf("%d", &t);
        if(t > heap[1]) {
            heap[1] = t;
            heap_adjust(1, h);
        }
    }

    if(n&1)    printf("%.1lf\n", heap[1]*1.0);
    else {
        heap[2] = heap[2] > heap[3] ? heap[3] : heap[2];
        printf("%.1lf\n", (heap[1]*1.0 + heap[2]*1.0)/2);
    }
    }
    return 0;
}