uva 10148 - Advertisement(区间选点问题）

题目连接：10148 - Advertisement

题目大意：给出目标数和n个行人， 让后给出n个人的移动方向（从某一站移动到另外一站）， 现在要粘贴广告在一些站台上，要使得每个行人看到的广告数尽量接近目标。

解题思路：典型的区间选点问题，见算法入门经典P153.

#include <stdio.h>
#include <string.h>
#include <algorithm>
using namespace std;
const int N = 10000;

struct way {
    int x;
    int y;
}w[N];
int sum, n, Min, Max, cnt, vis[N * 2 + 10];

bool cmp(const way& a, const way&b) {
    if (a.y != b.y) return a.y < b.y;
    else    return a.x > b.x;
}

void input() {
    Min = 1 < 30, Max = 0;
    int p, q;
    scanf("%d%d", &sum, &n);
    for (int i = 0; i < n; i++) {
	scanf("%d%d", &p, &q);
	if (p > q)
	    w[i].x = q, w[i].y = p;
	else
	    w[i].x = p, w[i].y = q;
	if (w[i].y > Max)   Max = w[i].y;
	if (w[i].x < Min)   Min = w[i].x;
    }
}

int solve() {
    int cnt = 0, now;
    memset(vis, 0, sizeof(vis));
    for (int i = 0; i < n; i++) {
	now = 0;
	for (int j = w[i].x; j <= w[i].y; j++)
	    if (vis[j + N]) now++;

	now = sum - now;

	for (int j = w[i].y; j >= w[i].x && now > 0; j--)
	    if (vis[j + N] == 0) {
		vis[j + N] = 1;
		now--;
		cnt++;
	    }
    }
    return cnt;
}

int main() {
    int cas;
    scanf("%d", &cas);
    while (cas--) {
	input();
	sort(w, w + n, cmp);

	printf("%d\n", solve());
	for (int i = Min; i <= Max; i++)
	    if (vis[i + N]) printf("%d\n", i);

	if (cas)    printf("\n");
    }
    return 0;
}