#11

largestproductinagrid.cpp

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

string s = 
"08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08\n\
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00\n\
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65\n\
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91\n\
22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80\n\
24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50\n\
32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70\n\
67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21\n\
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72\n\
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95\n\
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92\n\
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57\n\
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58\n\
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40\n\
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66\n\
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69\n\
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36\n\
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16\n\
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54\n\
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48";

using ull = unsigned long long;

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

ull dfs(vector<vector<int>> grid, int row, int col) {
    auto inrange = [&](int r, int c) { return (0 <= r && r < grid.size()) && (0 <= c && c < grid[0].size()); };
    if (!inrange(row, col))
        return 1;

    ull mP = 1, p = 1;
    for (int i = 0; i < 4; i++) {
        if (!inrange(row + i, col)) {
            p = 1;
            break;
        }
        p *= grid[row+i][col];
    }
    mP = max(mP, p);
    p = 1;
    for (int i = 0; i < 4; i++) {
        if (!inrange(row - i, col)) {
            p = 1;
            break;
        }
        p *= grid[row-i][col];
    }
    mP = max(mP, p);
    p = 1;
    for (int i = 0; i < 4; i++) {
        if (!inrange(row, col - i)) {
            p = 1;
            break;
        }
        p *= grid[row][col-i];
    }
    mP=max(mP,p);
    p=1;
    for(int i=0;i<4;i++){
        if(!inrange(row,col+i)){
            p=1;
            break;
        }
        p*=grid[row][col+i];
    }
    mP = max(mP, p);
    p = 1;
    for (int i = 0; i < 4; i++) {
        if (!inrange(row - i, col - i)) {
            p = 1;
            break;
        }
        p *= grid[row-i][col-i];
    }
    mP = max(mP, p);
    p = 1;
    for (int i=0;i<4;i++){
        if(!inrange(row-i,col+i)){
            p=1;
            break;
        }
        p*=grid[row-i][col+i];
    }
    mP=max(mP,p);
    p=1;
    for(int i=0;i<4;i++){
        if(!inrange(row+i,col+i)){
            p=1;
            break;
        }
        p*=grid[row+i][col+i];
    }
    mP=max(mP,p);
    p=1;
    for(int i=0;i<4;i++){
        if(!inrange(row+i,col-i)){
            p=1;
            break;
        }
        p*=grid[row+i][col-i];
    }
    mP=max(mP,p);
    return mP;
}

int main() {
    stringstream ss(s);
    vector<vector<int>> grid;
    for (std::string str; std::getline(ss, str); ) {
        vector<int> row;
        std::stringstream ss2(str);
        for (int x; ss2 >> x; ) {
            row.push_back(x);
        }
        grid.push_back(row);
    }
    ull maxProd = 1;
    for (int i = 0; i < grid.size(); i++) {
        for (int j = 0; j < grid[0].size(); j++) {
            maxProd = max(maxProd, dfs(grid, i, j));
        }
    }
    cout << maxProd;
}

optimized.cpp

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

string s = 
"08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08\n\
49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00\n\
81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65\n\
52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91\n\
22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80\n\
24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50\n\
32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70\n\
67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21\n\
24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72\n\
21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95\n\
78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92\n\
16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57\n\
86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58\n\
19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40\n\
04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66\n\
88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69\n\
04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36\n\
20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16\n\
20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54\n\
01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48";

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

int helper(vector<vector<int>> grid, int row, int col) {
    auto inrange = [&](int r, int c) { return (0 <= r && r < grid.size()) && (0 <= c && c < grid[0].size()); };
    if (!inrange(row, col))
        return 1;

    int mP = 1;
    for (int i = 0; i < 8; i++) {
        int p = 1;
        for (int k = 0; k < 4; k++) {
            if (!inrange(row + dy[i] * k, col + dx[i] * k)) {
                p = 1;
                break;
            }
            p *= grid[row+dy[i] * k][col+dx[i] * k];
        }
        mP = max(mP, p);
    }
    
    return mP;
}

int main() {
    stringstream ss(s);
    vector<vector<int>> grid;
    for (std::string str; std::getline(ss, str); ) {
        vector<int> row;
        std::stringstream ss2(str);
        for (int x; ss2 >> x; ) {
            row.push_back(x);
        }
        grid.push_back(row);
    }
    int maxProd = 1;
    for (int i = 0; i < grid.size(); i++) {
        for (int j = 0; j < grid[0].size(); j++) {
            maxProd = max(maxProd, helper(grid, i, j));
        }
    }
    cout << maxProd;
}