luogu 1053

来源：互联网发布：沈阳淘宝运营培训编辑：程序博客网时间：2024/06/09 19:07

篝火晚会(标签是图论和群论
看了题解打出来的, 不过还好搞懂了主要的点在代码中有注释

#include <cstdio>#include <algorithm>#define MAXN 50005using namespace std;int n, ans;int a[MAXN], b[MAXN];bool vis[MAXN];int c[MAXN];int t1[MAXN], t2[MAXN];int read() {    int f = 1, k = 0;    char c = getchar();    while (c < '0' || c > '9') {        if(c == '-') {            f = -1;        }        c = getchar();    }    while (c <= '9' && c >= '0') {        k = k * 10 + c - '0';        c = getchar();    }    return f * k;}int main() {    n = read();    for(int i = 1; i <= n; i ++) {        a[i] = read();        b[i] = read();    }    c[1] = 1;    c[2] = a[1];    vis[c[1]] = vis[c[2]] = true;    for(int i = 2; i < n; i ++) { //求出目标字串        if(c[i - 1] == a[c[i]]) c[i + 1] = b[c[i]];        else if(c[i - 1] == b[c[i]]) c[i + 1] = a[c[i]];        else {printf("-1"); return 0;}        vis[c[i + 1]] = true;    }    for(int i = 1; i <= n; i ++) {//判断是否都有位置        if(!vis[i]) {printf("-1"); return 0;}    }    for(int i = 1; i <= n; i ++) { // t1记录正着的, t2记录逆着的距离 , 最大的距离就是答案         int t = (c[i] - i + n) % n;        t1[t] ++;        ans = max(ans, t1[t]);        t = (c[n - i + 1] - i + n) % n;        t2[t] ++;        ans = max(ans, t2[t]);    }    printf("%d", n - ans);    return 0;}

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