细节&数组 Spiral Matrix II

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
            vector<vector<int>> res(n,vector<int>(n));
            int beginX = 0, endX = n-1;
            int beginY = 0, endY = n-1;
            int v = 1;
            while(true) {
                //from left to right
                for(int i=beginY; i<=endY; i++) {
                    res[beginX][i] = v;
                    v++;
                }
                if(++beginX > endX) break;
                //from top to bottom
                for(int i=beginX; i<=endX; i++) {
                    res[i][endY] = v;
                    v++;
                }
                if(--endY < beginY) break;
                //from right to left
                for(int i=endY; i>=beginY; i--) {
                    res[endX][i] = v;
                    v++;
                }
                if(--endX < beginX) break;
                //from bottom to top
                for(int i=endX; i>=beginX; i--) {
                    res[i][beginY] = v;
                    v++;
                }
                if(++beginY > endY) break;
            }
            return res;
    }
};