0-1 BFS

Resources:

Cf blog

Shakil Ahmed blog

cp_algorithm 

Youtube 

vjudge contest 

GFG 

Implementation:

	///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;
	}

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