Lost Cows（线段树） POJ - 2182

N (2 <= N <= 8,000) cows have unique brands in the range 1..N. In a spectacular display of poor judgment, they visited the neighborhood 'watering hole' and drank a few too many beers before dinner. When it was time to line up for their evening meal, they did not line up in the required ascending numerical order of their brands.

Regrettably, FJ does not have a way to sort them. Furthermore, he's not very good at observing problems. Instead of writing down each cow's brand, he determined a rather silly statistic: For each cow in line, he knows the number of cows that precede that cow in line that do, in fact, have smaller brands than that cow.

Given this data, tell FJ the exact ordering of the cows.

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题意：给出n头牛前面有多少头比他编号少的数目，求出原来的牛的编号，

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#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstring>
#include<stdio.h>
#include<algorithm>
#include<map>
#include<queue>
#include<set>
#include <sstream>
#include<vector>
#include<cmath>    
#include<stack>
#include<time.h>
#include<ctime>
using namespace std;
#define inf 1<<30
#define eps 1e-7
#define LD long double
#define LL long long
#define maxn 100000005    
int tree[maxn] = {};
int a[maxn] = {};
int b[maxn] = {};
void buildTree(int step,int L,int R)//建树
{
    if (L == R)
    {
        tree[step] = 1;
        return;
    }
    int mid = (L + R) >> 1;
    buildTree(step * 2, L, mid);
    buildTree(step * 2 + 1, mid + 1, R);
    tree[step] = tree[step * 2] + tree[step * 2 + 1];
}
int search(int step, int L, int R, int num)
{
    tree[step]--;//更新，当前位置减一
    if (L == R)
    {
        return L;
    }
    int mid = (L + R) / 2;
    if (num <= tree[step * 2])//在左子树范围
        search(step * 2, L, mid, num);
    else
        search(step * 2 + 1, mid + 1, R, num-tree[step*2]);//在右子树范围，减去左子树的个数
}
int main()
{
    int n;
    scanf("%d", &n);
    buildTree(1, 1, n);
    for (int i = 2; i <= n; i++)
    {
        scanf("%d", &a[i]);
    }
    a[1] = 0;
    for (int i = n; i >= 1; i--)//从后往前找，只有最后一个是确定的
    {
        b[i] = search(1, 1, n, a[i] + 1);//查找编号时要加一
    }
    for (int i = 1; i <= n; i++)
    {
        printf("%d\n", b[i]);
    }
}

 

 

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