59. Spiral Matrix II

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題目敘述

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

Example 1:

Input: n = 3 Output: [[1,2,3],[8,9,4],[7,6,5]]

Example 2:

Input: n = 1 Output: [[1]]

解題思路

Solution

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] ans = new int[n][n];
        int count = 1;

        int left = 0, right = n - 1, top = 0, bottom = n - 1;
        while (left <= right && top <= bottom) {
            for (int i = left; i <= right; i++) {
                ans[top][i] = count++;
            }
            top++;
            
            for (int i = top; i <= bottom; i++) {
                ans[i][right] = count++;
            }
            right--;
            
            if (top <= bottom) {
                for (int i = right; i >= left; i--) {
                    ans[bottom][i] = count++;
                }
                bottom--;
            }
            
            if (left <= right) {
                for (int i = bottom; i >= top; i--) {
                    ans[i][left] = count++;
                }
                left++;
            }
        }
        
        return ans;
    }
}