Enter the "Basic Training of Deep Search" and step into the palace of C++ algorithms (4)

The fourth question appears on the screen:

[Search and Backtracking Algorithm] Largest Platform (Standard IO)

Time limit: 1000 ms Space limit: 262144 KB

Topic description:

The following is a 4×4 matrix. Its characteristics are: (1) The elements of the matrix are all positive integers; (2) Elements with equal values ​​are adjacent. In this way, this matrix forms a first-level "platform" with the largest "platform" area of ​​8 and a height (element value) of 6. If there is an N×N matrix that also has the characteristics of the above matrix, find the area and height of the largest "platform" of the matrix.
6 6 6 7
1 6 3 7
1 6 6 7
6 6 7 7

enter:

The first line is N (1≤N≤100), and the following is an N×N matrix.

Output:

The first line is the maximum area of ​​the platform;
the second line is the element value.

Sample input:

4
6 6 6 7
1 6 3 7
1 6 6 7
6 6 7 7

Sample output:

8
6

 "It should still be a search. The condition is that it is above, below, left, and right of the current platform, and the numbers are equal... " Xiaohang said.

#include<iostream>
using namespace std;
int n,plat[105][105],check[150],ans,maxx=-1,num,lnum;
void dg(int x,int y)
{
    ++ans;
    plat[x][y]=0;
    if(plat[x+1][y]==lnum) dg(x+1,y);
    if(plat[x-1][y]==lnum) dg(x-1,y);
    if(plat[x][y+1]==lnum) dg(x,y+1);
    if(plat[x][y-1]==lnum) dg(x,y-1);
}
int main()
{
    check[0]=1;
    cin>>n;
    for(int i=1;i<=n;++i)
    {
        for(register int j=1;j<=n;++j)
        {
            cin>>plat[i][j];
        }
    }
    for(int i=1;i<=n;++i)
    {
        for(int j=1;j<=n;++j)
        {
            if(check[plat[i][j]]==0)
            {
                lnum=plat[i][j];
                ans=0;
                dg(i,j);
                if(ans>maxx)
                {
                    maxx=ans;
                    num=lnum;
                }
                check[plat[i][j]]=1;
            }
        }
    }
    cout<<maxx<<endl<<num;
}

The code came out quickly, and 100 points followed quickly. The fifth question popped up in an instant...