[LeetCode] Spiral Matrix II

题目描述:

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 ]
]

解题思路:

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int>> matrix(n ,vector<int>(n, 0));
        if (n == 0) {
            return matrix;
        }
        int left = 0;
        int right = n - 1;
        int up = 0;
        int down = n - 1;
        
        int count = n * n;
        int ii = 0;
        
        while (true) {

            for (int i = left; i <= right; ++i) {
                matrix[up][i] = ++ii;
            }
            if (ii >= count) {
                break;
            }
            
            up += 1;
            for (int i = up; i <= down; ++i) {
                matrix[i][right] = ++ii;
            }
            if (ii >= count) {
                break;
            }
            
            right -= 1;
            for (int i = right; i >= left; --i) {
                matrix[down][i] = ++ii;
            }
            if (ii >= count) {
                break;
            }
        
            down -= 1;
            for (int i = down; i >= up; --i) {
                matrix[i][left] = ++ii;
            }
            left += 1;
            
            if (ii >= count) {
                break;
            }
        }
        
        return matrix;
    }
};