leetcode 6.ZigZag Convertion

class Solution {
public:
    string convert(string s, int numRows) {
        if(numRows > s.size() || s.size() < numRows) return s;
        int numCols = s.size()/(2*numRows-2)*(numRows-2+1)+(s.size()%numRows?1:0);
        char **a = new char* [numRows];
        for(int i = 0; i < numRows; ++i) a[i] = new char[numCols]();
        int i = 0, j = 0, k = 0;
        int flag = 1;
        for(; j < numCols, k < s.size(); ++j) {
            if(!flag) j = j - 1;
            for(; k < s.size(), i < numRows; ++i, ++k) {
                a[i][j] = s[k];
                flag = 0;
            }
            i = i - 2;
            j = j + 1;
            for(; j % (numRows-1) && k < s.size(); ++j, ++k, --i) {
                a[i][j] = s[k];
            }
        }
        string res = "";
        for(i = 0; i < numRows; ++i) {
            for(j = 0; j < numCols; ++j) {
                if(a[i][j] != 0) {
                    res += a[i][j];
                }
            }
        }
        res += '\0';
        cout << res << endl;
        delete [] a[i];
        delete [] a;
        return res;
    }    
};

我在本地测试的问啥问题，提交出现以下问题：

大佬们有没有遇到过这种错误？？？