PAT 1013 Battle Over Cities (dfs seeking connected component)

It is vitally important to have all the cities connected by highways in a war. If a city is occupied by the enemy, all the highways from/toward that city are closed. We must know immediately if we need to repair any other highways to keep the rest of the cities connected. Given the map of cities which have all the remaining highways marked, you are supposed to tell the number of highways need to be repaired, quickly.

For example, if we have 3 cities and 2 highways connecting city1-city2 and city1-city3. Then if city1 is occupied by the enemy, we must have 1 highway repaired, that is the highway city2-*cit**y*3.

Input Specification:

Each input file contains one test case. Each case starts with a line containing 3 numbers N (<1000), M and K, which are the total number of cities, the number of remaining highways, and the number of cities to be checked, respectively. Then M lines follow, each describes a highway by 2 integers, which are the numbers of the cities the highway connects. The cities are numbered from 1 to N. Finally there is a line containing K numbers, which represent the cities we concern.

Output Specification:

For each of the K cities, output in a line the number of highways need to be repaired if that city is lost.

Sample Input:

Sample Output:

1
0
0

Thinking

After a given a map, blocking a point, to make the rest of the points Unicom, seeking to add a minimum number of roads.

After labeling with a flag array point is accessed, a point can be determined using dfs blocked, Unicom component block number of the figure (not block communication). The answer is block-1.

The last set of data is a time-out, can answer the next block map records a point, can be reused.

This problem can also continue to optimize the time complexity, but should be directly over the PAT.

Code

#include <stdio.h>
#include <string>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <string.h>
#include <algorithm>
#include <cmath>
#include <map>
#include <limits.h> 
using namespace std;
int maze[1000+10][1000+10];
int N, M, K;
int block = 0;
bool flag[1000+10];
void dfs(int index){
    flag[index] = 1;
    for(int i = 1; i <= N; i++){
        if(maze[i][index] && !flag[i])  dfs(i);
    }
}
map<int, int> mmp;
int main() {
    cin >> N >> M >> K;
    int e, s;
    for(int i = 0; i < M; i++){
        cin >> e >> s;
        maze[e][s] = 1;
        maze[s][e] = 1;
    }
    for(int i = 0; i < K; i++){
        cin >> e;
        block = 0;
        if(mmp.count(e)){
            cout << mmp[e] << endl;
            continue;
        }
        memset(flag, 0, sizeof(flag));
        flag[e] = 1;
        for(int j = 1; j <= N; j++){
            if(!flag[j]){
                block++;
                dfs(j);
            }
        }
        mmp[e] = block - 1;
        cout << block - 1 << endl;
    }
    return 0; 
}