[wikioi]四色问题

http://wikioi.com/problem/1116/

典型的DFS。

#include <iostream>

#include <memory.h>



#define LEN 8

using namespace std;



int graph[LEN][LEN];

int color[LEN]; // 1,2,3,4 for 4 colors

int ans = 0;

int n = 0;



void dfs(int step) {

    if (step == n) {

        ans++;

        return;

    }

    for (int x = 1; x <= 4; x++) {

        bool valid = true;

        for (int i = 0; i < step; i++) {

            if (graph[i][step] == 1 && color[i] == x) {

                valid = false;

                break;

            }

        }

        if (valid) {

            color[step] = x;

            dfs(step+1);

            color[step] = 0;

        }

    }

}

 

int main()

{

    memset(graph, 0, sizeof(graph));

    memset(color, 0, sizeof(color));

    cin >> n;

    for (int i = 0; i < n; i++) {

        for (int j = 0; j < n; j++) {

            cin >> graph[i][j];

        }

    }

    dfs(0);

    cout << ans << endl;

    return 0;

}