Submission #1097975

#	Time	Username	Problem	Language	Result	Execution time	Memory
1097975		anhthi	K-th path (IZhO11_kthpath)	C++14	0 / 100	1 ms	348 KiB

kthpath

#include <bits/stdc++.h>
 
using namespace std;
 
#define fi first
#define se second
#define ll long long
#define mp(x, y) make_pair(x, y)
#define sz(v) ((int) (v).size())
#define all(v) (v).begin(), (v).end()
#define MASK(i) (1LL << (i))
#define BIT(x, y) (((x) >> (y)) & 1)
#define pb push_back
#define heap priority_queue
#define max_rng *max_element
#define min_rng *min_element
#define rep(i, n) for(int i = 1, _n = (n); i <= _n; ++i)
#define forn(i, a, b) for(int i = (a), _b = (b); i <= _b; ++i)
#define ford(i, a, b) for(int i = (a), _b = (b); i >= _b; --i)

 
template <class X, class Y>
    inline bool maximize(X &x, Y y) {
        return (x < y ? x = y, true : false);
    }
 
template <class X, class Y>
    inline bool minimize(X &x, Y y) {
        return (x > y ? x = y, true : false);
    }
 
template <class X>
    inline void compress(vector<X> &a) {
        sort(all(a));
        a.resize(unique(all(a)) - a.begin());
    }
 
int ctz(ll x) { return __builtin_ctzll(x); }
int lg(ll x) { return 63 - __builtin_clzll(x); }
int popcount(ll x) { return __builtin_popcount(x); }
 
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rand(ll l, ll r) {
    return l + abs((ll) rng()) % (r - l + 1);
}
 
const ll oo = (ll) 3e18;
const int inf = (ll) 1e9 + 7, mod = (ll) 1e9 + 7;
 
const int N = 65, LOG = 16;
 
void add(int &x, int y) { x += y; if (x >= mod) x -= mod; }
void sub(int &x, int y) { x -= y; if (x < 0) x += mod; }

int n, m;
char a[N][N];
ll k;

ll kCn[N][N];
ll valid[N][N], temp[N][N];

int dx[] = {0, 1};
int dy[] = {1, 0};

bool isIn(int x, int y) {
    return 1 <= x && x <= n && 1 <= y && y <= m;
}

vector<pair<int, int>> cur[26];

int main(void) {
 
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    
    cin >> n >> m;
    rep(i, n) rep(j, m) cin >> a[i][j];
    cin >> k;

    if (k == 1) {
        return cout << a[1][1], 0;
    }
    #define plus(x, y) { x += y; minimize(x, oo); }
    #define mul(x, y) (x >= oo / y ? oo : x * y)
    #define get(i, j) kCn[i + j - 2][i - 1]

    forn(i, 0, n + m) {
        kCn[i][0] = 1;
        forn(j, 1, i) {
            kCn[i][j] = kCn[i-1][j] + kCn[i-1][j-1];
            minimize(kCn[i][j], oo);
        }
    }

    memset(valid, 0, sizeof valid);

    string res;
    res += a[1][1];
    valid[1][2] = valid[2][1] = 1;

    forn(len, 2, n + m - 1) {
        forn(i, 0, 25) cur[i].clear();
        forn(i, 1, n) forn(j, 1, m) if (valid[i][j]) {
            cur[a[i][j] - 'a'].pb(mp(i, j));
        }
        int real = -1;
        forn(i, 0, 25) {
            ll total = 0;
            for (pair<int, int> nxt : cur[i]) {
                plus(total, mul(valid[nxt.fi][nxt.se], get(n - nxt.fi + 1, m - nxt.se + 1)));
            }
            if (total < k) k -= total;
            else {
                real = i;
                break;
            }
        }
        assert(real != -1);
        res += ((char) (real + 'a'));
        for (pair<int, int> nxt : cur[real]) {
            forn(t, 0, 1) {
                int x = nxt.fi + dx[t];
                int y = nxt.se + dy[t];
                if (!isIn(x, y)) continue;
                plus(temp[x][y], valid[nxt.fi][nxt.se]);
            }
        }
        forn(i, 1, n) forn(j, 1, m) valid[i][j] = temp[i][j];
        memset(temp, 0, sizeof temp);
    }

    cout << res;

    return 0;
}

• Subtask 1: 0 / 100