问string1 +“|”+ string2 是什么意思

EN

#include <iostream>
#include <climits>
#include <unordered_map>
#include <algorithm>
using namespace std;

// N x N matrix
#define N 5

// create a map to store solutions of subproblems
 unordered_map<string, string> lookup;

// Function to check if cell (i, j) is a valid cell or not
bool isValid(int i, int j)
{
return (i >= 0 && i < N && j >= 0 && j < N);
}

  // Find longest path starting from cell (i, j) formed by adjacent 
 // numbers in the matrix
string findLongestPath(int mat[N][N], int i, int j)
{
// if the cell is invalid
if (!isValid (i, j))
    return 0;

// construct a unique map key from dynamic elements of the input
string key = to_string(i) + "|" + to_string(j);

// if sub-problem is seen for the first time, solve it and 
// store its result in a map
if (lookup.find(key) == lookup.end())
{
    // string to store path starting (i, j)
    string path;

    // recurse top cell if its value is +1 of value at (i, j)
    if (i > 0 && mat[i - 1][j] - mat[i][j] == 1)
        path = findLongestPath(mat, i - 1, j);

    // recurse right cell if its value is +1 of value at (i, j)
    if (j + 1 < N && mat[i][j + 1] - mat[i][j] == 1)
        path = findLongestPath(mat, i, j + 1);

    // recurse bottom cell if its value is +1 of value at (i, j)
    if (i + 1 < N && mat[i + 1][j] - mat[i][j] == 1)
        path = findLongestPath(mat, i + 1, j);

    // recurse left cell if its value is +1 of value at (i, j)
    if (j > 0 && mat[i][j - 1] - mat[i][j] == 1)
        path = findLongestPath(mat, i, j - 1);

    // note that as matrix contains all distinct elements,
    // there is only one path possible from current cell

    lookup[key] = to_string(mat[i][j]) + " - " +  path;
}

// return path starting from (i, j)
 return lookup[key];
}