HDU

HDU - 5353

为什么我在自己演自己啊， 加了个特判结果下一次正确的时候没有把图清空， 找了半天bug。

先枚举一条边的状态就能推出全部， 输出过程用拓扑排序。

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize(4)
#include<bits/stdc++.h>
#define LL long long
#define LD long double
#define ull unsigned long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ALL(x) (x).begin(), (x).end()
#define fio ios::sync_with_stdio(false); cin.tie(0);

using namespace std;

const int N = 1e5 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;
const double PI = acos(-1);

template<class T, class S> inline void add(T &a, S b) {a += b; if(a >= mod) a -= mod;}
template<class T, class S> inline void sub(T &a, S b) {a -= b; if(a < 0) a += mod;}
template<class T, class S> inline bool chkmax(T &a, S b) {return a < b ? a = b, true : false;}
template<class T, class S> inline bool chkmin(T &a, S b) {return a > b ? a = b, true : false;}

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

int n, a[N];
int tmp[N];
vector<int> G[N];
vector<PII> ret;
int deg[N];
LL ave;
int b[N];

bool dfs(int u, int op) {
    int nex = (u + 1) % n;
    if(nex) {
        if(op == -1) {
            a[nex]++;
            a[u]--;
            G[u].push_back(nex);
            deg[nex]++;
            if(a[nex] == ave) return dfs(nex, 0);
            else if(a[nex] == ave + 1) return dfs(nex, -1);
            else if(a[nex] == ave - 1) return dfs(nex, 1);
            else return false;
        }
        else if(op == 0) {
            if(a[nex] == ave) return dfs(nex, 0);
            else if(a[nex] == ave + 1) return dfs(nex, -1);
            else if(a[nex] == ave - 1) return dfs(nex, 1);
            else return false;
        }
        else if(op == 1) {
            a[nex]--;
            a[u]++;
            G[nex].push_back(u);
            deg[u]++;
            if(a[nex] == ave) return dfs(nex, 0);
            else if(a[nex] == ave + 1) return dfs(nex, -1);
            else if(a[nex] == ave - 1) return dfs(nex, 1);
            else return false;
        }
    }
    else {
        if(op == -1) {
            a[nex]++;
            a[u]--;
            G[u].push_back(nex);
            deg[nex]++;
        }
        else if(op == 1) {
            a[nex]--;
            a[u]++;
            G[nex].push_back(u);
            deg[u]++;
        }
        return a[nex] == ave;
    }
}

bool solve() {
    ave = 0;

    for(int i = 0; i < n; i++) {
        ave += a[i];
    }
    if(ave % n) return false;
    ave /= n;

    for(int i = 0; i < n; i++) {
        if(abs(a[i] - ave) > 2) {
            return false;
        }
    }

    bool flag = false;

    for(int op = -1; op <= 1; op++) {
        for(int i = 0; i < n; i++) {
            a[i] = tmp[i];
            G[i].clear();
            deg[i] = 0;
        }
        if(dfs(0, op)) {
            flag = true;
            break;
        }
    }
    return flag;
}

int main() {
    int T; scanf("%d", &T);
    while(T--) {
        scanf("%d", &n);
        ret.clear();
        for(int i = 0; i < n; i++) {
            deg[i] = 0;
            G[i].clear();
            scanf("%d", &a[i]);
            tmp[i] = a[i];
        }

        if(!solve()) {
            puts("NO");
            continue;
        }

        queue<int> que;
        for(int i = 0; i < n; i++) {
            if(!deg[i]) {
                que.push(i);
            }
        }

        for(int i = 0; i < n; i++) b[i] = tmp[i];

        while(!que.empty()) {
            int u = que.front();
            que.pop();
            for(auto &v : G[u]) {
                deg[v]--;
                ret.push_back(mk(u, v));
                b[u]--;
                b[v]++;
                if(!deg[v]) {
                    que.push(v);
                }
            }
        }

        puts("YES");
        printf("%d
", SZ(ret));
        for(auto &t : ret) {
            printf("%d %d
", t.fi + 1, t.se + 1);
        }
    }
    return 0;
}

/*

*/