Leetcode zigzag Conversion

class Solution {public:    string convert(string s, int nRows) {        int len = s.length();        if (len < 2 || nRows == 1 || len < nRows) return s;        vector<string> cols;        int si = 0;        int ri = 0;                while (si < len) {            bool inacol = cols.size() % (nRows-1) == 0;                        if (!inacol) {                for (int i=0; i<nRows - 2 && si <len; i++, si++) {                    cols.push_back(s.substr(si, 1));      // a char as a single column                }                continue;            }                        cols.push_back(string());            for (int i=0; i<nRows && si<len; i++, si++) {                cols.back().push_back(s[si]);   // all char in a column            }        }        string res;        int nCols = cols.size();        int stepa = nRows - 1;        int stepb = 0;                for (int i=0; i<nRows; i++) {            bool usea = false;            int last = -1;            for (int j = 0; j < nCols; j += usea ? stepa : stepb) {                usea = !usea;                if (j == last) continue;                last = j;                                int r = i, c = j;                                if (cols[c].length() < 1) break;                                if (c % (nRows - 1) != 0) {                    r = 0;                } else if (cols[c].length() - 1 < r) {                    break;                }                res.push_back(cols[c][r]);            }            --stepa, ++stepb;        }        cols.clear();        return res;    }};

In general, this is so long, and the time is 100 MS + code is not good!

 

The following code finds a problem that has not been noticed before:

    string a("abc");    string b;    b.push_back(a[10]);    cout<<b.length()<<endl;

Compiling and running will not report an error. Although the [10] operation is obviously out of bounds, different from the array, when the subscript operation of the string is out of bounds, a null character will be returned. Go to http://www.cplusplus.com/and check the following statement:

IfPosIs equal to the string length, the function returns a reference to a null character (Chart ()).

From the actual test, it is not only when Pos = Str. Length () in STR [POS], but also when it is larger than the string length. Although this process is helpful, sometimes it makes it harder to discover errors. The following code:

    string a("abc");    string b(a);    b.push_back(a[10]);        cout<<a<<","<<b<<endl;    cout<<(a == b)<<endl;

When outputting A and B, they are exactly the same. However, because B is more NULL than a, It is very confusing to have them equal in the equivalent comparison. Of course, the root cause is that codenong is not careful...