http://acm.pku.edu.cn/JudgeOnline/problem?id=1154
第一題不是用暴力過的哦，嘿嘿
//深度優先搜索
#include?<iostream>
using?namespace?std;
struct?dfs
{
????int?row,?col;
????int?dire;
}path[100000];//為什么用*path會發生運行錯誤,不能執行path[i]的訪問.
int?out(char?p[21][21],?int?row,?int?col)
{
????int?dire;
????int?result;
????int?top;
????int?t;
????int?record[26]?=?{0};
????int?i,?j,?g,?h;
????int?incr[4][2]?=?{?{0,?1},?{1,?0},?{0,?-1},?{-1,?0}};
????top?=?1;
????dire?=?0;
????i?=?j?=?0;
????path[top].row?=?i;
????path[top].col?=?j;
????/**//***************************************
????*?課本的這里是path[top].dire?=?dire;即=0;但是path[top]中表示的dire是當前top點在前一頂點的方位.
????*?故在題目中當top?=?1時path[top].dire表示它相對于top?=?0時的方位,當path[top]改變時說明已經返回到了top?=?0?處.
????*?即top?=?1遍歷完畢;但當path[top].dire?=?0；此時+1?=?1?而不是=?4?所以函數并沒有中斷循環.
????*?此時top--?，所以top?=?0;會出現path[0]指向第一定點，而path[1]則指向了第二個定點而產生錯誤.
????
????***************************************/
????path[top].dire?=?3;??//path[top].dire?=?dire;
????record[p[i][j]?-?'A']++;
????result?=?0;
????while(top?>?0?||?dire?<?4)
????{
????????if(dire?<?4)
????????{
????????????g?=?i?+?incr[dire][0];
????????????h?=?j?+?incr[dire][1];
????????????t?=?p[g][h]?-?'A';
????????????if(g?>=?0&&g?<?row&&?h?>=?0&&?h?<?col?&&record[t]?==?0)
????????//????if(record[t]?==?0)剛開始因這樣而出錯
????????????{
????????????????record[t]++;
????????????????top++;
????????????????path[top].row?=?g;
????????????????path[top].col?=?h;
????????????????path[top].dire?=?dire;
????????????????i?=?g;?j?=?h;?dire?=?0;
????????????}
????????????else{
????????????????dire++;
????????????}
????????}
????????else{
????/**//*????????
????cout?<<?top?<<?endl;
????????????????for(i?=?1;?i?<=?top;?i++)
????????????????????cout?<<?path[i].row?<<?"?"?<<?path[i].col?<<?endl;
????????????????????*/
????????????dire?=?path[top].dire?+?1;
????????????t?=?p[path[top].row][path[top].col]?-?'A';
????????????record[t]--;
????????????if(result?<?top){
????????????????result?=?top;
????????????}
????????????top--;
????????????if(top?>?0){
????????????????i?=?path[top].row;
????????????????j?=?path[top].col;
????????????}
????????}
????}
????return?result;
}
int?main()
{
????int?i;
????int?row,?col;
????int?result;
????char?p[21][21];
????cin?>>?row?>>?col;
????for(i?=?0;?i?<?row;?i++)
????????cin?>>?p[i];
????result?=?out(p,?row,?col);
????cout?<<?result?<<?endl;
????return?0;
}