面试经典150题——Day35

一、题目

54. Spiral Matrix

Given an m x n matrix, return all elements of the matrix in spiral order.

Example 1:

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

Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

Constraints:

m == matrix.length
n == matrix[i].length
1 <= m, n <= 10
-100 <= matrix[i][j] <= 100

二、题解

确定边界，进行模拟

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        int m = matrix.size();
        int n = matrix[0].size();
        vector<int> res;
        //左边界，右边界，上边界，下边界
        int left = 0,right = n - 1,up = 0,down = m - 1;
        while(true){
            //从左到右
            for(int j = left;j <= right;j++) res.push_back(matrix[up][j]);
            //上边界下移
            if(++up > down) break;
            //从上到下
            for(int i = up;i <= down;i++) res.push_back(matrix[i][right]);
            //右边界左移
            if(--right < left) break;
            //从右到左
            for(int j = right;j >= left;j--) res.push_back(matrix[down][j]);
            //下边界上移
            if(--down < up) break;
            //从下到上
            for(int i = down;i >= up;i--) res.push_back(matrix[i][left]);
            //左边界右移
            if(++left > right) break;
        }
        return res;
    }
};