Leetcode:59. Spiral Matrix II

Description

Given an integer n, generate a square matrix filled with elements from 1 to n^2 in spiral order.

Example

Given n = 3,

You should return the following matrix:
[
    [ 1, 2, 3 ],
    [ 8, 9, 4 ],
    [ 7, 6, 5 ]
]

思路

• 没啥好说的，一圈一圈的打印

代码

cclass Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int>> res(n, vector<int>(n, 0));
        
        int start = 0;
        int sum = 1;
        while(start * 2 < n){
           generate(res, n, start, sum);
           start++;
        }
        
        return res;
    }
    
    void generate(vector<vector<int>>& res, int n, int start, int &count){
        int endCol = n - start - 1;
        int endRow = n - start - 1;
                
        for(int i = start; i <= endCol; ++i)
            res[start][i] = count++;
                
        if(endRow > start){
            for(int i = start + 1; i <= endRow; ++i)
                res[i][endCol] = count++;
        }
                
        if(endCol > start){
            for(int i = endCol - 1; i >= start; --i)
                res[endRow][i] = count++;
        }
                
        if(endRow > start && endCol > start){
            for(int i = endRow - 1; i > start; --i)
                res[i][start] = count++;
        }
    }
};