https://www.acwing.com/problem/content/39/ 直接模拟

java
class Solution {
    public int[] printMatrix(int[][] matrix) {
        if(matrix == null || matrix .length == 0 || matrix[0].length == 0) {
            return new int[0];
        }
        
        int row = matrix.length;
        
        int col = matrix[0].length;
        
        int top = 0;
        int bot = row - 1;
        int left = 0;
        int right = col - 1;
        
        int index = 0;
        
        
        int[] result = new int[row * col];
        
        while(left <= right && top <= bot) {
            for(int i = left; i <= right; i++) {
                result[index++] = matrix[top][i]; 
            }
            
            top++;
            
            for(int i = top; i <= bot; i++) {
                result[index++] = matrix[i][right];
            }
            
            right--;
            
            
            if(top <= bot) {
                for(int i = right; i >= left; i--) {
                    result[index++] = matrix[bot][i];
                }
                
                bot--;
            }
            
            if(left <= right) {
                for(int i = bot; i >= top; i--) {
                    result[index++] = matrix[i][left];
                }
                
                left++;
            }
            
            
        }
        
        return result;
        
    }
}