vector 开动态二维、三维数组_vector.reserve 开辟三维数组

 vector<vector<int>> a(n, vector<int>(m)); // n 行 m 列 的二维数组

行和列的下标都是从0开始，即（0 ~ n - 1 , 0 ~ m - 1）;  数组元素值默认为 0。

 vector<vector<int>> a(n, vector<int>(m, value)); // n 行 m 列 的二维数组

初始化为value。

例题：Problem - C - Codeforces

#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
 
const int N = 2e5 + 10;
int n, m;
typedef pair<int, int>PII;
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
 
    int t;
    cin >> t;
    while(t--)
    {
        cin >> n >> m;
        vector<vector<int>> a(n, vector<int>(m)), b(n, vector<int>(m)); // n * m 的二维数组
        for(int i = 0; i < n; i++)
            for(int j = 0; j < m; j++)
                {
                    cin >> a[i][j];
                    b[i][j] = a[i][j];
                }
 
        for(int i = 0; i < n; i++)
            sort(a[i].begin(), a[i].end());
        
        int cnt = 0;
        bool ok = true;
        set<PII>st;
        for(int i = 0; i < n; i++)
        {
            cnt = 0;
            int l = 0, r = 0;
            for(int j = 0; j < m; j++)
            {
                if(a[i][j] != b[i][j]) 
                {
                    cnt++;
                    if(l == 0) l = j + 1;
                    else r = j + 1;
                }
            }
            if(cnt >= 3) ok = false;
            else if(cnt == 2) st.insert({l, r});
        }
       if(!ok) cout << "-1" << endl;
       else
       {
        if(st.size() == 0) cout << 1 << " " << 1 << endl;
        else if(st.size() == 1) {
            int l, r;
            for(auto p : st){
                l = p.first, r = p.second;
            }
            ok = false;
            for(int i = 0; i < n; i++)
                if(b[i][l - 1] < b[i][r - 1]) ok = true;
                if(ok) cout << "-1" << endl;
                else cout << l << " " << r << endl;
            }
             else cout << "-1" << endl;
        }
       
    }
 
    return 0;
}

vector 开三维数组

// d[n + 1][m + 1][5] = {INF}
 vector< vector < vector<int> > > d(n + 1,vector< vector<int> >(m + 1,vector<int>(5,INF)));
  
// vis[n + 1][m + 1][5] = {false}
  vector< vector < vector<bool> > > vis(n + 1,vector< vector<bool> >(m + 1,vector<bool>(5,false)));

vector dp(N+1,vector(K+1,vector<long long>(D,-1)));
 
dp[N][K][D]