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01987.cpp
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01987.cpp
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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int r, c;
vector<vector<char> > a;
vector<bool> alpha(26, false);
int backtrack(int x, int y, int cnt) {
if (x == r-1 && y == c-1) return cnt;
int ret = cnt;
if (x > 0 && !alpha[a[x-1][y]-'A']) {
alpha[a[x-1][y]-'A'] = true;
ret = max(ret, backtrack(x-1, y, cnt+1));
alpha[a[x-1][y]-'A'] = false;
}
if (x < r-1 && !alpha[a[x+1][y]-'A']) {
alpha[a[x+1][y]-'A'] = true;
ret = max(ret, backtrack(x+1, y, cnt+1));
alpha[a[x+1][y]-'A'] = false;
}
if (y > 0 && !alpha[a[x][y-1]-'A']) {
alpha[a[x][y-1]-'A'] = true;
ret = max(ret, backtrack(x, y-1, cnt+1));
alpha[a[x][y-1]-'A'] = false;
}
if (y < c-1 && !alpha[a[x][y+1]-'A']) {
alpha[a[x][y+1]-'A'] = true;
ret = max(ret, backtrack(x, y+1, cnt+1));
alpha[a[x][y+1]-'A'] = false;
}
return ret;
}
void solve(void) {
cin >> r >> c;
a.resize(r, vector<char>(c));
for (int i=0; i<r; i++) {
for (int j=0; j<c; j++) {
cin >> a[i][j];
}
}
alpha[a[0][0]-'A'] = true;
cout << backtrack(0, 0, 1);
}
int main(void) {
ios::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
solve();
return 0;
}