std::string convert(std::string s, int numRows) {

if(s.size() <= 1 || numRows < 2) return s;

std::vector<std::string> sVec(numRows);

bool down = true;

for( int i = 0, j = 0, iEnd = s.size(); i < iEnd; ++i) {

sVec[j].push_back(s[i]);

j = down? j+1:j-1;

if(j == numRows) {

j = numRows - 2;

down = false;

}

else if(j < 0) {

j = 1;

down = true;

}

}

std::string result;

for(auto&& value : sVec) {

result.append(value);

}

return result;

}

{

if (s.size() <= 1 || nRows <= 1) return s;

std::string result;

//第一行元素

for (int i = 0, iEnd = s.size(); i < iEnd; i += nRows*2-2)

result.append(1, s[i]);

//中间元素

for (int r = 1; r < nRows-1; ++r)

{

const int steps = 2 * nRows - 2 * r - 2;

for (int i = r, iEnd = s.size(), k = 0; i < iEnd;)

{

result.append(1, s[i]);

if (k++ % 2 == 0)

i += steps;

else

i += r*2;

}

}

//最后一行元素

for (int i = nRows - 1, iEnd = s.size(); i < iEnd; i += nRows * 2 - 2)

result.append(1, s[i]);

return result;