[leetcode 59] Spiral Matrix II

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本文介绍了一个生成螺旋矩阵的算法，该算法接收一个整数n作为输入，并返回一个n×n的矩阵，矩阵中的元素从1到n²按螺旋顺序填充。通过四个方向的循环迭代，实现了矩阵的螺旋填充。

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

class Solution {
public:
    vector<vector<int> > generateMatrix(int n) {
        vector<vector<int> > res(n, vector<int>(n, 0));
        if (n == 0) {
            return res;
        }
        int beginX = 0, endX = n - 1;
        int beginY = 0, endY = n - 1;
        int cnt = 1;
        while (cnt <= n*n) {
            for (int i = beginX; i <= endX; i++) {
                res[beginY][i] = cnt++;
            }
            beginY++;
            for (int i = beginY; i <= endY; i++ ) {
                res[i][endX] = cnt++;
            }
            endX--;
            for (int i = endX; i >= beginX; i--) {
                res[endY][i] = cnt++;
            }
            endY--;
            for (int i = endY; i >= beginY; i--) {
                res[i][beginX] = cnt++;
            }
            beginX++;
        }
        return res;
    }
};