uva169 - Graph Coloring （回溯）

题意：
给你一个图，让你然后染成黑色和白色，尽可能多的节点染成黑色，但相邻节点不能都是黑色。
思路：
node[i]=1即将i节点染成黑色，为0则表示为白色，默认所有节点为白色，总共就黑白两种情况 ，Judge可以了就黑色，然后白色。回溯。
代码如下:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
//hei 1  -- bai 0

const int N = 105;
int n, m, maxn;
int node[N], ege[N][N],ans[N];
int Judge(int u) {
    for (int i = 1; i <= n; i++) 
        if (ege[u][i] && node[i])
            return false;
    return true;
}
void dfs(int cur) {
    if (cur == n +1) {
        int temp = 0;
        for (int i = 1; i <= n; i++) {
            if (node[i])
                temp++;
        }
        if (maxn < temp) {
            maxn = temp;
            int j = 0;
            for (int i = 1; i <= n; i++) 
                if (node[i])
                    ans[j++] = i;
        }
        return;
    }
    node[cur] = 1;
    if (Judge(cur))
        dfs(cur + 1);
    node[cur] = 0;
    dfs(cur + 1);
}
int main() {
    int cas;
    scanf("%d", &cas);
    while (cas--) {
        memset(ege, 0, sizeof(ege));
        memset(node, 0, sizeof(node));
        memset(ans, 0, sizeof(ans));
        scanf("%d%d", &n, &m);
        int u, v;
        for (int i = 1; i <= m; i++) {
            scanf("%d%d", &u, &v);
            ege[u][v] = ege[v][u] = 1;
        }
        maxn = -1;
        dfs(1);
        printf("%d\n%d", maxn, ans[0]);
        for (int i = 1; i < maxn; i++) {
            if (ans[i])
                printf(" %d", ans[i]);
        }
        printf("\n");
    }
}