【POJ】Buy Tickets（线段树）

点更新用法很巧妙的一道题。倒序很容易的找到该人的位置，而update操作中需要不断的变化下标才能合理的插入。看了别人写的代码，学习了。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <map>
using namespace std;

const int maxn = 2e5 + 10;
int sumv[maxn << 2], data[maxn];

void PushUp (int rt) {
    sumv[rt] = sumv[rt << 1] + sumv[rt << 1 | 1];
}

void build (int l, int r, int rt) {
    if (l == r) {
        sumv[rt] = 1;
        return ;
    }
    int m = (l + r) / 2;
    build (l, m, rt << 1);
    build (m + 1, r, rt << 1 | 1);
    PushUp (rt);
}

void update (int p, int v, int l, int r, int rt) {
    if (l == r) {
        data[l] = v; sumv[rt] = 0;
        return ;
    }
    int m = (l + r) >> 1;
    if (sumv[rt * 2] >= p) {
        update (p, v, l, m, rt * 2);
    } else {
        update (p - sumv[rt * 2], v, m + 1, r, rt * 2 + 1);
    }
    PushUp(rt);
}

int main () {
    pair<int, int> p[maxn];
    int n;
    while (~scanf ("%d", &n)) {
        for (int i = 0; i < n; ++ i) {
            scanf ("%d%d", &p[i].first, &p[i].second);
        }
        build (1, n, 1);
        for (int i = n - 1; i >= 0; -- i) {
            update (p[i].first + 1, p[i].second, 1, n, 1);
        }
        for (int i = 1; i <= n; ++ i) {
            if (i == 1) {
                printf ("%d", data[i]);
            } else {
                printf (" %d", data[i]);
            }
        }
        puts("");
    }
    return 0;
}