0-1BFS.cpp

///https://www.spoj.com/problems/KATHTHI/
// Topic: 0-1 bfs
#include <bits/stdc++.h>
using namespace std;
#define INF 1<<30
#define endl '\n'
#define maxn 1000005
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
typedef long long ll;
const double PI = acos(-1.0);
const ll mod = 1e9 + 7;

inline void normal(ll &a) { a %= mod; (a < 0) && (a += mod); }
inline ll modMul(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a * b) % mod; }
inline ll modAdd(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a + b) % mod; }
inline ll modSub(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); a -= b; normal(a); return a; }
inline ll modPow(ll b, ll p) { ll r = 1; while (p) { if (p & 1) r = modMul(r, b); b = modMul(b, b); p >>= 1; } return r; }
inline ll modInverse(ll a) { return modPow(a, mod - 2); }
inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }


///**
template < typename F, typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
  return os << "(" << p.first << ", " << p.second << ")";
}

template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if ( it != v.begin() ) os << ", ";
    os << *it;
  }
  return os << "}";
}

template < typename T >
ostream &operator << ( ostream & os, const set< T > &v ) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if ( it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "]";
}

template < typename F, typename S >
ostream &operator << ( ostream & os, const map< F, S > &v ) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if ( it != v.begin() ) os << ", ";
    os << it -> first << " = " << it -> second ;
  }
  return os << "]";
}

#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)

clock_t tStart = clock();
#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)

void faltu () { cerr << endl; }

template <typename T>
void faltu( T a[], int n ) {
  for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
  cerr << endl;
}

template <typename T, typename ... hello>
void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }
// Program showing a policy-based data structure.
#include <ext/pb_ds/assoc_container.hpp> // Common file 
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less 
#include <iostream>
using namespace __gnu_pbds;
using namespace std;
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
        tree_order_statistics_node_update>
        new_data_set;

// find_by_order(k) – ফাংশনটি kth ordered element এর একটা পয়েন্টার রিটার্ন করে। অর্থাৎ তুমি চাইলেই kth ইন্ডেক্সে কি আছে, সেটা জেনে ফেলতে পারছো!
// order_of_key(x) – ফাংশনটি x এলিমেন্টটা কোন পজিশনে আছে সেটা বলে দেয়।

//*//**___________________________________________________**/


bool is_valid(int a, int b, int c, int d)
{
  return (a >= 0 && a < c && b >= 0 && b < d);
}

int main()
{
  FASTIO
  ///*
#ifndef ONLINE_JUDGE
  freopen("in.txt", "r", stdin);
  freopen("out.txt", "w", stdout);
  freopen("error.txt", "w", stderr);
#endif
//*/
  int T;
  //scanf("%d", &T);
  T = 1;
  cin >> T;
  for (int cs = 1; cs <= T; cs++) {
    int n, m;
    cin >> n >> m;
    vector<string> str(n);
    for (int i = 0; i < n; i++) cin >> str[i];

    int vis[n][m];
    for (int i = 0; i < n; i++)
      for (int j = 0; j < m; j++) vis[i][j] = INT_MAX;

    deque<pair<int, int>> dQ;
    vis[0][0] = 1;
    dQ.push_front({0, 0});

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

    while (!dQ.empty()) {
      auto it = dQ.front();
      dQ.pop_front();
      int x = it.first;
      int y = it.second;
      if (x == n - 1 && y == m - 1) break;
      for (int i = 0; i < 4; i++) {
        int r = it.first + dx[i];
        int c = it.second + dy[i];

        if (is_valid(r, c, n, m)) {
          if (str[r][c] == str[x][y] && vis[r][c] > vis[x][y]) {
            vis[r][c] = vis[x][y];
            dQ.push_front({r, c});
          }
          else if ( vis[r][c] > vis[x][y] + 1) {
            vis[r][c] = vis[x][y] + 1;
            dQ.push_back({r, c});
          }
        }
      }
    }

    cout << vis[n - 1][m - 1] - 1 << endl;
  }
  return 0;
}