Description

　　問題在這：鏈接

　　測試樣例在這：鏈接

　　還有些特殊的測試樣例需要測試，可以在題目下的 DISCUSS 裏翻一翻。

思路

　　問題概述如下：

　　我們需要考慮，如何拆墻才是最優的。是拆最長的墻的嗎？並不是的，因為最長的墻可能對之後要走的列沒有幫助。如何讓拆掉的墻對之後的列幫助最大呢？最優的辦法就是讓拆掉的墻的右端盡可能的長，那麽當魔術師走之後的列的時候FQ就會更少。

　　代碼如下，雖然WA，但是過了DISCUSS中的所有測試樣例，之後想到了會再改：

#include<iostream>
#include<algorithm>
#include
 
<cstring>
#include<vector>
using namespace std;
#define INT_MIN -9999
bool map[MAX_X + 1][MAX_Y + 1]; //true 有墻, false 無墻
int n, k; //總墻數與魔術師能翻過的墻數

struct Point {
    int x;
    int y;
};

struct Wall {
    Point start;
    Point end;
    bool remove_flag;
};

int greedy_remove (const int& max_x, const
 
 int& max_y, vector<Wall>& w) {
    //cout << " 進入 greedy_remove "<< max_x << " " << max_y << " " << n << " " << k << endl;
    int remove_counter = 0;
    for (int i = 0; i <= max_x; i++) {
        int energy = k;
        for (int j = 0
 
; j <= max_y; j++) {
            if (!map[i][j])
                continue;
            else if (map[i][j] && energy) {
                energy--;
                continue;
            }
            else if (map[i][j] && !energy) {
                int dist = INT_MIN; //阻礙前進的墻的最右端到當前位置的距離
                int num = INT_MIN; //需要刪除的墻的序號
                for (int m = 1; m <= n; m++) {
                    if (!w[m].remove_flag && w[m].end.x >= i && w[m].start.x <= i) {
                        int dist2 = w[m].end.x - i;
                        //貪心選擇當前列到墻最右端最遠的墻
                        if (dist < dist2) {
                            num = m;
                            dist = dist2;
                        }
                    }
                }
                //刪墻
                if (num != INT_MIN) {
                    for (int i2 = w[num].start.x; i2 <= w[num].end.x; i2++) {
                        map[i2][w[num].start.y] = false;
                    }
                    w[num].remove_flag = true;
                    remove_counter++;    
                }
            }
        } //j <= max_y
    } //i <= max_x
    return remove_counter;
} //int greedy_remove()

int main(void) {
    int t;
    cin >> t;
    vector<Wall> w;
    while (t--) {
        cin >> n >> k;
        //建墻
        memset(map, 0, sizeof(map));
        int max_x = INT_MIN, max_y = INT_MIN; 
        w.resize(n+1);
        for (int i = 1; i <= n; i++) {
            int x1, y1, x2, y2;
            cin >> x1 >> y1 >> x2 >> y2;
            if (x1 <= x2) {
                for (int j = x1; j <= x2; j++){
                    map[j][y1] = true;
                }
                w[i].start.x = x1;
                w[i].start.y = y1;
                w[i].end.x = x2;
                w[i].end.y = y2;
                bool remove_flag = false;
            }
            else if (x1 > x2){
                for (int j = x2; j <= x1; j++) {
                    map[j][y2] = true;
                }
                w[i].start.x = x2;
                w[i].start.y = y2;
                w[i].end.x = x1;
                w[i].end.y = y1;
                bool remove_flag = false;
            }
            if (max_x < std::max(x1, x2)) {
                max_x = std::max(x1, x2);
            }
            if (max_y < std::max(y1, y2)) {
                max_y = std::max(y1, y2);
            }
        }
        //貪心刪墻
        int ans = greedy_remove(max_x, max_y, w);
        w.clear();
        vector<Wall>().swap(w);
        cout << ans << endl;
    }
    return 0;
} //int main()

POJ #1230 Pass-Muraille 貪心