spiral-matrix-ii[螺旋数组]

题目描述

Given an integer n, generate a square matrix filled with elements from 1 to n 2 in spiral order.
For example,
Given n =3,
You should return the following matrix:
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]

• 思路
  螺旋保存二维数组值。
  设置上、右、下、左四个变量，然后每次循环填数并更新对应的变量即可。

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] map = new int[n][n];
        if(n <= 0)
            return map;
        
        int num = 1;
        int up = 0;
        int right = n-1;
        int down = n-1;
        int left = 0;
        while(num <= n*n){
            for(int i=up; i<=right; i++){
                map[up][i] = num;
                num ++;
            }
            up ++;
            
            for(int i=up; i<=down; i++){
                map[i][right] = num;
                num ++;
            }
            right --;
            
            for(int i=right; i>=left; i--){
                map[down][i] = num;
                num ++;
            }
            down --;
            
            for(int i=down; i>=up; i--){
                map[i][left] = num;
                num ++;
            }
            left ++;
        }
        
        return map;
    }
}