LeetCode--54. Spiral Matrix-蒲公英云

LeetCode--54. Spiral Matrix

灰太狼 2022-08-21 13:49 239阅读 0赞

Problem:

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.
For example,
Given the following matrix:
[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5].
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Analysis:

题目理解：
    将一维或二维数组中的元素按顺时针放向进行打印；
解题分析：
    1. 模拟；
    2. 递归：
    1）每次重新计算最开始的左上初始点；
    2）然后依此遍历最上一行，最右一列，最后一行，以及最左一行；
    3）注意避免重复遍历，处理好边界问题；

Answer:
递归解法：

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> list = new ArrayList<Integer>();
        if(matrix.length==0 || matrix[0].length==0) return list;
        int m = matrix.length, n = matrix[0].length;
        spiral_print(0,m-1,0,n-1,matrix,list);
        return list;
    }
    public static void spiral_print(int row_start,int row_end,int col_start,int col_end,int[][] matrix,List<Integer> list){
        if (row_start>row_end || col_start>col_end) return;
        for(int i=col_start;i<=col_end;i++){
            list.add(matrix[row_start][i]);
        }
        if(row_start+1>row_end) return;
        for(int i=row_start+1;i<=row_end;i++){
            list.add(matrix[i][col_end]);
        }
        if(col_start+1>col_end) return;
        for(int i=col_end-1;i>=col_start;i--){
            list.add(matrix[row_end][i]);
        }
        for(int i=row_end-1;i>row_start;i--){
            list.add(matrix[i][col_start]);
        }
        spiral_print(row_start+1,row_end-1,col_start+1,col_end-1,matrix,list);
    }
}

迭代解法：

public class Solution {
public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> result = new ArrayList<Integer>();
        if(matrix.length == 0) return result;
        int left=0,right=matrix[0].length-1,top=0,bottom=matrix.length-1,direction=0;
        while(left <= right && top <= bottom){
            if(direction == 0){
                for(int i=left;i<= right;i++){
                    result.add(matrix[top][i]);
                }
                top++;
            }
            else if(direction == 1){
                for(int i=top;i<=bottom;i++){
                    result.add(matrix[i][right]);
                }
                right--;
            }
            else if(direction == 2){
                for(int i=right;i>=left;i--){
                    result.add(matrix[bottom][i]);
                }
                bottom--;
            }
            else if(direction == 3){
                for(int i=bottom;i>=top;i--){
                    result.add(matrix[i][left]);
                }
                left++;
            }
            direction=(direction+1) % 4;
        }
    return result;
}
}