看不懂的代码

#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>

using namespace std;

typedef long long llint;
typedef pair< int, int > par;
#define x first
#define y second

class StringGame {
public:
  int a[55][55];
  int ch[55], dead[55];

  vector <int> getWinningStrings( vector <string> S ) {
    vector< int > ans;
    int n = S.size();
    for( int i = 0; i < n; ++i )
      for( int j = 0; j < (int)S[i].size(); ++j )
        a[i][S[i][j]-'a']++;
    
    for( int i = 0; i < n; ++i ) {
      for( int j = 0; j < 55; ++j )
        ch[j] = dead[j] = 0;
      
      bool okk = true;
      for( int j = 0; j < 26; ++j ) {
        int z = -1;
        for( int k = 0; k < 26; ++k )
          if( !ch[k] ) {
            int ok = 1;
            for( int l = 0; l < n; ++l )
              if( !dead[l] && a[l][k] > a[i][k] ) { ok = 0; break; }
            if( ok ) { z = k; break; }
          }
        if( z == -1 ) { okk = false; break; }
        for( int l = 0; l < n; ++l )
          if( a[l][z] < a[i][z] ) dead[l] = 1;
        ch[z] = 1;
      }
      
      for( int l = 0; l < n; ++l )
        if( l != i && !dead[l] ) okk = false;
      if( okk ) ans.push_back( i );
    }
    return ans;
  }
};