leetcode 59. Spiral Matrix II
z
 2018-05-19 10:36:10  

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

Example:

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Input: 3
Output:
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]
  • 设定left， right， up， down, 来指定当前的上下左右边界。
  • 在不超过边界的前提下，依次从左到右，从上到下，从右到左，从下到上遍历。
  • 注意输入参数小于0的情况。
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class Solution {
    public int[][] generateMatrix(int n) {
        if (n<=0) return new int[0][0];
        int content = 1;
        int i=0, j = 0;
        int up = 0;
        int down = n-1;
        int left = 0;
        int right = n-1;
        int[][] ans = new int[n][n];
        while(i>=up && i<=down && j>=left && j<= right){
            while(j<=right){
                ans[i][j] = content;
                content ++;
                j++;
            }
            up ++;
            j--;
            i++;
            while(i<=down){
                ans[i][j] = content;
                i++;
                content++;
            }
            right --;
            i--;
            j--;
            while(j>= left){
                ans[i][j] = content;
                j --;
                content ++;
            }
            down --;
            j++;
            i--;
            while(i>= up){
                ans[i][j] = content;
                i --;
                content ++;
            }
            left ++;
            i++;
            j++;
        }
        return ans;
    }
}

python

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