leetcode2397. 被列覆盖的最多行数 回溯法/枝剪

第一次手搓一个回溯法，超时后采用枝剪勉强通过

class Solution {
    int max=0;
    int numSelect;
    public int maximumRows(int[][] matrix, int numSelect) {
        Set<String>stateSet=new HashSet<>();
        dfs(matrix,new boolean[matrix[0].length],0,numSelect,stateSet);
        return max;
    }
    public void dfs(int[][]matrix,boolean[]selected,int step,int numSelect,Set<String>stateSet){
        String currentState = Arrays.toString(selected);
        if (stateSet.contains(currentState))
            return;
        else
            stateSet.add(currentState);

        if(step==numSelect){
            int cnt=0;
            for(int i=0;i<matrix.length;i++){
                boolean flag=true;
                for(int j=0;j<matrix[0].length;j++){
                    if(matrix[i][j]!=0&&!selected[j]){
                        flag=false;
                        break;
                    }
                }
                if(flag)
                    cnt++;
            }
            max=Math.max(max,cnt);
                return;
        }
        for(int i=0;i<selected.length;i++){
                if(!selected[i]){
                    selected[i]=true;
                    dfs(matrix,selected,step+1,numSelect,stateSet);
                    selected[i]=false;
                }
        }
    }
}