Home Coding Leetcode Medium

⭐️⭐️

# 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]]

# Solution

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int>> res(n, vector<int>(n, 0));
        int left = 0, right = n-1, up = 0, down = n-1;
        int val = 1;
        while (left <= right && up <= down) {
            for (int j=left; j<=right; j++) {
                res[up][j] = val;
                val++;
            }
            up++;
            if (up > down) break;
            for (int i=up; i<=down; i++) {
                res[i][right] = val;
                val++;
            }
            right--;
            if (left > right) break;
            for (int j=right; j>=left; j--) {
                res[down][j] = val;
                val++;
            }
            down--;
            if (up > down) break;
            for (int i=down; i>= up; i--) {
                res[i][left] = val;
                val++;
            }
            left++;
            if (left > right) break;
        }
        return res;
    }
};
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;
    }
}