LeetCode OJ:Spiral Matrix II

Spiral Matrix II

 

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>> result(n);
        for(int i=0;i<n;i++)result[i].resize(n);
        int x1 = 0;
        int y1 = 0;
        int x2 = n-1;
        int y2 = n-1;
        int cnt = 1;
        while(x1 <= x2 && y1 <= y2)
        {
            //up row
            for(int i = y1; i <= y2; ++i) result[x1][i]=cnt++;
            //right column
            for(int i = x1+1; i <= x2; ++i) result[i][y2]=cnt++;
            //bottom row
            if(x2 != x1)
            for(int i = y2-1; i >= y1; --i) result[x2][i]=cnt++;
            //left column
            if(y1 != y2)
            for(int i = x2-1; i > x1; --i) result[i][y1]=cnt++;
            
            x1++, y1++, x2--, y2--;
        }

        return result;
    }
};



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