leetcode解题: Spiral Matrix II (59)

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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:

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

解法1：

Java

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public class Solution {
    public int[][] generateMatrix(int n) {
        int level = (n + 1) / 2;
        int[][] res = new int[n][n];
        // fill by level
        
        int num = 1;
        for (int i = 0; i < level; ++i) {
            int lastrow = n - i - 1;
            int lastcol = n - i - 1;
            
            // move right
            for (int j = i; j <= lastcol; ++j) {
                res[i][j] = num;
                num++;
            }
            
            // move down
            for (int j = i + 1; j <= lastrow; ++j) {
                res[j][lastcol] = num;
                num++;
            }
            
            // move left
            for (int j = lastcol - 1; j >= i; --j) {
                res[lastrow][j] = num;
                num++;
            }
            
            // move up
            for (int j = lastrow - 1; j > i; --j) {
                res[j][i] = num;
                num++;
            }
        }
        
        return res;
    }
}