In this HackerRank Travelling Salesman in a Grid problem solution, The traveling salesman has a map containing m*n squares. He starts from the top left corner and visits every cell exactly once and returns to his initial position (top left). The time taken for the salesman to move from a square to its neighbor might not be the same. Two squares are considered adjacent if they share a common edge and the time is taken to reach square b from square a and vice-versa is the same. Can you figure out the shortest time in which the salesman can visit every cell and get back to his initial position?
Problem solution in Python.
#!/bin/python3
import os
import sys
#
# Complete the tspGrid function below.
#
INF = 10 ** 9
m = True, False, None
TT, TF, TN, FT, FF, FN, NT, NF, NN = ((i, j) for i in m for j in m)
m, n = map(int, input().split())
row = [list(map(int, input().split())) for i in range(m)]
column = [list(map(int, input().split())) for j in range(m - 1)]
def minimize(t, v):
global current, INF
current[t] = min(v, current.get(t, INF))
if m & n & 1:
ans = 0
else:
ans = INF
previous, current = {}, {NN[:1] * (m + n): 0}
for i in range(m):
for j in range(n):
previous, current, k = current, {}, m + j - 1 - i
for state, value in previous.items():
l, x, r = state[:k], state[k: k + 2], state[k + 2:]
if x == NN:
if i + 1 < m and j + 1 < n:
minimize(l + TF + r, value)
elif x == NT or x == NF:
value += column[i - 1][j]
if j + 1 < n:
minimize(state, value)
if i + 1 < m:
minimize(l + x[::-1] + r, value)
elif x == FN or x == TN:
value += row[i][j - 1]
if j + 1 < n:
minimize(l + x[::-1] + r, value)
if i + 1 < m:
minimize(state, value)
else:
value += row[i][j - 1] + column[i - 1][j]
if x == TF:
if i + 1 == m and j + 1 == n:
ans = min(ans, value)
elif x == FT:
minimize(l + NN + r, value)
elif x == TT:
count = 1
index = -1
while count:
index += 1
count += 1 if r[index] == TT[0] else -1 if r[index] == FF[0] else 0
minimize(l + NN + r[:index] + TT[:1] + r[index + 1:], value)
else:
count = -1
index = k
while count:
index -= 1
count += 1 if l[index] == TT[0] else -1 if l[index] == FF[0] else 0
minimize(l[:index] + FF[:1] + l[index + 1:] + NN + r, value)
print(ans)
Problem solution in Java.
import java.io.*;
import java.util.*;
public class Solution {
static int[] three;
static int bit(int s, int i) {
return s/three[i]%3;
}
static final int NS = 5798;
static int ns = 0;
static int[] mapping = new int[177147];
static int[] states = new int[NS];
static void dfs(int k, int x, int s) {
if (k == 0) {
if (x == 0) {
mapping[s] = ns;
states[ns++] = s;
}
return;
}
dfs(k-1, x, 3*s);
if (x > 0) {
dfs(k-1, x-1, 3*s+1);
}
dfs(k-1, x+1, 3*s+2);
}
static int n;
static int[] cur;
static void tr(int j, int s, int g, int opt) {
s -= three[j]*bit(s, j)+three[j+1]*bit(s, j+1);
s += three[j]*g;
if (j == n-1) {
if (bit(s, n) > 0) {
return;
}
s *= 3;
}
cur[mapping[s]] = Math.min(cur[mapping[s]], opt);
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
BufferedWriter bw = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
StringTokenizer st = new StringTokenizer(br.readLine());
int m = Integer.parseInt(st.nextToken());
n = Integer.parseInt(st.nextToken());
if (n%2 > 0 && m%2 > 0) {
bw.write("0");
bw.newLine();
bw.close();
br.close();
return;
}
int[][] horizontal = new int[m > n ? m : n][n];
for (int i = 0; i < m; i++) {
st = new StringTokenizer(br.readLine());
for (int j = 0; j < n - 1; j++) {
int item = Integer.parseInt(st.nextToken());
horizontal[i][j] = item;
}
}
int[][] vertical = new int[m > n ? m : n][n];
for (int i = 0; i < m - 1; i++) {
st = new StringTokenizer(br.readLine());
for (int j = 0; j < n; j++) {
int item = Integer.parseInt(st.nextToken());
vertical[i][j] = item;
}
}
three = new int[n+1];
three[0] = 1;
for (int i = 0; i < n; i++) {
three[i+1] = three[i]*3;
}
dfs(n+1, 0, 0);
int[][] tr4 = new int[ns][n];
int[][] tr8 = new int[ns][n];
for (int si = 0; si < ns; si++) {
int s = states[si];
for (int i = 0; i < n; i++) {
int g = bit(s, i)+3*bit(s, i+1);
if (g == 4) {
int c = 0;
for (int j = i+1; ; j++) {
int b = bit(s, j);
if (b == 1) c++;
if (b == 2) c--;
if (c == 0) {
tr4[si][i] = s-three[i]*g-three[j]; // 1122 -> 0012
break;
}
}
}
if (g == 8) {
int c = 0;
for (int j = i; ; j--) {
int b = bit(s, j);
if (b == 1) c++;
if (b == 2) c--;
if (c == 0) {
tr8[si][i] = s-three[i]*g+three[j]; // 1122 -> 1200
break;
}
}
}
}
}
int[][] dp = new int[2][ns];
int[] pre = dp[0];
cur = dp[1];
Arrays.fill(cur, 0, ns, Integer.MAX_VALUE/2);
cur[mapping[0]] = 0;
for (int i = 0; i < m; i++)
for (int j = 0; j < n; j++) {
int[] tmp = pre;
pre = cur;
cur = tmp;
Arrays.fill(cur, 0, ns, Integer.MAX_VALUE/2);
for (int si = 0; si < ns; si++) {
int s = states[si];
int g = bit(s, j)+bit(s, j+1)*3;
int opt = pre[si];
switch (g) {
case 0:
tr(j, s, 1+3*2, opt + vertical[i][j] + horizontal[i][j]);
break;
case 1:
case 3:
tr(j, s, 1, opt + vertical[i][j]);
tr(j, s, 3, opt + horizontal[i][j]);
break;
case 2:
case 6:
tr(j, s, 2, opt + vertical[i][j]);
tr(j, s, 6, opt + horizontal[i][j]);
break;
case 5:
tr(j, s, 0, opt);
break;
case 4:
tr(j, tr4[si][j], 0, opt);
break;
case 8:
tr(j, tr8[si][j], 0, opt);
break;
case 7:
if (i == m-1 && j == n-1)
tr(j, s, 0, opt);
break;
}
}
}
bw.write(String.valueOf(cur[mapping[0]]));
bw.newLine();
bw.close();
br.close();
}
}
Problem solution in C++.
#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <ctime>
using namespace std;
typedef long long ll;
class DisjointSet{
public:
DisjointSet( int size ){
rank.resize( size, 0 );
p.resize( size, -1 );
elem.resize( size, 0 );
}
void makeSet( int x ){
p[x] = x;
rank[x] = 0;
elem[x] = 1;
}
bool isSet( int x, int y ) {
return !( p[x]<0 || p[y]<0 );
}
bool Union( int x, int y ){
if ( isSameSet(x,y) ) return false;
link( findSet(x), findSet(y) );
return true;
}
int findSet( int x ){
if ( x != p[x] ) p[x] = findSet( p[x] );
return p[x];
}
bool isSameSet( int x, int y ){
return ( findSet(x) == findSet(y) );
}
vector<int> rank, p, elem;
void link ( int x, int y ){
if ( rank[x] > rank[y] ){
p[y] = x;
elem[x] += elem[y];
} else {
p[x] = y;
elem[y] += elem[x];
if ( rank[x] == rank[y] ) rank[y]++;
}
}
};
inline bool bit(ll x, ll b)
{
return ((x>>b)&1)==1;
}
static unordered_map<ll,vector<ll>> memo;
vector<ll>& Next(int r, ll cur, bool first)
{
if ( memo.count(cur) ) return memo[cur];
ll w = cur&((1LL<<32)-1), g = cur>>32;
vector<ll> next;
for ( int i = 0; i < (1<<r); i++ ) {
ll a = w<<1, b = i<<1;
bool valid = true;
for ( int j = 0; j <= r; j++ ) {
ll a0 = a&3, b0 = b&3;
if ( a0==0&&b0==0 || a0==3&&b0==3 || a0==1&&b0==2 || a0==2&&b0==1 ) {
valid = false;
break;
}
a>>=1;
b>>=1;
}
if ( !valid ) {
continue;
}
DisjointSet d(2*r);
for ( int j = 0; j < r; j++ ) {
if ( bit(w,j) ) d.makeSet(j);
if ( bit(i,j) ) d.makeSet(j+r);
if ( bit(w,j) && bit(i,j) ) {
d.Union(j,j+r);
}
}
for ( int j = 0; j < r; j++ ) {
if ( !bit(w,j) ) continue;
for ( int k = j+1; k < r; k++ ) {
if ( !bit(w,k) ) continue;
if ( ((g>>(3*j))&7) == ((g>>(3*k))&7) ) {
d.Union(j,k);
}
}
}
for ( int j = 1; j < r; j++ ) {
if ( bit(i,j-1) && bit(i,j) ) {
if ( !d.Union(j+r-1, j+r) ) {
valid = false;
break;
}
}
}
if ( !valid ) {
continue;
}
bool checked[32] = {0};
for ( int j = 0; j < r; j++ ) {
if ( !bit(w,j) || checked[d.findSet(j)] ) continue;
bool connedted = false;
for ( int k = 0; k < r; k++ ) {
if ( !bit(i,k) ) continue;
if ( d.findSet(j) == d.findSet(k+r) ) {
checked[d.findSet(j)] = true;
connedted = true;
break;
}
}
if ( !connedted ) {
valid = false;
break;
}
}
if ( !valid ) {
continue;
}
ll gn[16] = {0};
int ig = 0;
map<ll,ll> mp;
for ( int j = 0; j < r; j++ ) {
if ( !bit(i,j) ) continue;
if ( mp.count(d.findSet(j+r)) ) {
gn[j] = mp[d.findSet(j+r)];
} else {
mp[d.findSet(j+r)] = ig;
gn[j] = ig;
ig++;
}
}
ll t = 0;
for ( int j = r-1; j >= 0; j-- ) {
t <<= 3;
t += gn[j];
}
next.push_back( (t<<32) + i );
}
return memo[cur] = next;
}
ll Count(int r, int c)
{
memo.clear();
if ( r > c ) swap(r,c);
map<ll,ll> dp;
dp[0] = 1;
for ( int i = 0; i < c; i++ ) {
map<ll,ll> dp2;
for ( auto p : dp ) {
auto& next = Next(r, p.first, i==0);
for ( auto nn : next ) {
dp2[nn] += p.second;
}
}
dp.swap(dp2);
}
ll sum = 0;
for ( auto it = dp.begin(); it != dp.end(); ++it ) {
ll w = it->first&((1LL<<32)-1);
w <<= 1;
bool valid = true;
for ( int j = 0; j <= r; j++ ) {
if ( (w&3) == 0 ) {
valid = false;
break;
}
w >>= 1;
}
if ( !valid ) {
continue;
}
ll g = it->first>>32;
if ( g ) {
continue;
}
sum += it->second;
}
return sum;
}
ll Solve(int r, int c, vector<vector<ll>>& ch, vector<vector<ll>>& cv)
{
memo.clear();
map<ll,ll> dp;
dp[0] = 0;
for ( int i = 0; i < c; i++ ) {
map<ll,ll> dp2;
for ( auto p : dp ) {
auto cur = p.first;
for ( auto next : Next(r, cur, i==0) ) {
ll cost = p.second;
for ( int j = 0; j < r; j++ ) {
if ( bit(cur,j) ^ bit(next,j) ) {
cost += cv[j][i];
}
}
ll t = next<<1;
for ( int j = 0; j <= r; j++ ) {
if ( bit(t,j) ^ bit(t,j+1) ) {
cost += ch[j][i];
}
}
if ( dp2.count(next)==0 || dp2[next] > cost ) {
dp2[next] = cost;
}
}
}
dp.swap(dp2);
}
ll ans = -1;
for ( auto it = dp.begin(); it != dp.end(); ++it ) {
ll w = it->first&((1LL<<32)-1);
w <<= 1;
bool valid = true;
for ( int j = 0; j <= r; j++ ) {
if ( (w&3) == 0 ) {
valid = false;
break;
}
w >>= 1;
}
if ( !valid ) {
continue;
}
ll g = it->first>>32;
if ( g ) {
continue;
}
ll cost = it->second;
for ( int j = 0; j < r; j++ ) {
if ( bit(it->first,j) ) {
cost += cv[j].back();
}
}
if ( ans < 0 || ans > cost ) {
ans = cost;
}
}
if ( ans < 0 ) return 0;
return ans;
}
int main()
{
int n = 0, m = 0;
cin >> m >> n;
vector<vector<ll>> ch, cv;
for ( int i = 0; i < m; i++ ) {
vector<ll> v(n-1,0);
for ( int j = 0; j < n-1; j++ ) {
cin >> v[j];
}
ch.push_back(v);
}
for ( int i = 0; i < m-1; i++ ) {
vector<ll> v(n,0);
for ( int j = 0; j < n; j++ ) {
cin >> v[j];
}
cv.push_back(v);
}
cout << Solve(m-1,n-1,ch,cv) << endl;
return 0;
}