Submission #488982

#	Time	Username	Problem	Language	Result	Execution time	Memory
488982		SirCovidThe19th	K-th path (IZhO11_kthpath)	C++17	100 / 100	1 ms	332 KiB

kthpath

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define f first
#define s second

int n, m; ll k, ways[35][35], choose[65][65]; pll range[35][35]; 
char A[35][35]; vector<char> ans;

int main(){
    cin >> n >> m;
	for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) cin >> A[i][j];
    cin >> k;

    for (int i = 0; i < 65 and (choose[i][0] = 1); i++)
        for (int j = 1; j <= i; j++)
            choose[i][j] = choose[i - 1][j] + choose[i - 1][j - 1];

    ans.push_back(A[1][1]); ways[1][1] = 1; range[1][1] = {1, choose[n + m - 2][n - 1]}; 

    for (int len = 2; len <= n + m - 1; len++){
        vector<pii> test; ll rangeSt = 0, tot = 0;
        for (int i = min(len, n), j = max(len - n + 1, 1); i and j <= m; i--, j++){
            pll R = {};
            if (ways[i - 1][j]) R = range[i - 1][j];
            if (ways[i][j - 1]) R = range[i][j - 1];
            if (k >= R.f and k <= R.s){ //a potential spot
                test.push_back({i, j}); rangeSt = R.f;
                ways[i][j] += ways[i - 1][j] + ways[i][j - 1];
            }
        }
        for (char c = 'a'; c <= 'z'; c++){
            for (pii i : test) if (A[i.f][i.s] == c)
                tot += ways[i.f][i.s] * choose[(n - i.f) + (m - i.s)][(m - i.s)];
            for (pii i : test) if (A[i.f][i.s] == c){
                pll R = {rangeSt, rangeSt + tot - 1};
                if (k >= R.f and k <= R.s){
                    if (ans.size() < len) ans.push_back(c);
                    range[i.f][i.s] = R;
                }
                else ways[i.f][i.s] = 0; //bad spot
            }
            rangeSt += tot; tot = 0;
        }
    }
	for (char c : ans) cout<<c;
}

Compilation message (stderr)

kthpath.cpp: In function 'int main()':
kthpath.cpp:41:36: warning: comparison of integer expressions of different signedness: 'std::vector<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   41 |                     if (ans.size() < len) ans.push_back(c);
      |                         ~~~~~~~~~~~^~~~~

• Subtask 1: 100 / 100