LeetCode 59. Spiral Matrix II (Java版; Medium)-蒲公英云

LeetCode 59. Spiral Matrix II (Java版; Medium)

朱雀 2023-07-03 06:06 203阅读 0赞

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LeetCode Top Interview Questions 59. Spiral Matrix II (Java版; Medium)

题目描述

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.
Example:
Input: 3
Output:
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

第一次做; 和剑指29题的顺时针打印很像, 核心: 1)确定圈数, 2)确定每圈打印的起点及剩余三个顶点的坐标

/* 核心: 模拟螺旋的过程; 确定好打印几圈? 每一圈的打印起点? */
class Solution { 
    public int[][] generateMatrix(int n) { 
        int[][] arr = new int[n][n];
        //打印几圈
        int loops = (n+1)/2;
        int num = 1;
        for(int i=0; i<loops; i++){ 
            //每一圈打印的起点(i,i)
            //左到右; i-0 = n-1-y -> y=n-1-i
            for(int col=i; col<=n-1-i; col++){ 
                arr[i][col] = num++;
            }
            //上到下, 上开下闭; i-0=n-1-ROW -> ROW=n-1-i
            for(int row=i+1; row<=n-1-i; row++){ 
                arr[row][n-1-i] = num++;
            }
            //右到左, 右开左闭; n-1-col = COL-0 -> COL=i
            for(int col=n-1-i-1; col>=i; col--){ 
                //n-1-row = i-0
                arr[n-1-i][col] = num++;
            }
            //下到上, 下开上开; n-1-row=i-0 -> row=n-1-i
            for(int row=n-1-i-1 ; row>i; row--){ 
                arr[row][i] = num++;
            }
        }
        return arr;
    }
}

力扣优秀题解

format_png

class Solution { 
    public int[][] generateMatrix(int n) { 
        int l = 0, r = n - 1, t = 0, b = n - 1;
        int[][] mat = new int[n][n];
        int num = 1, tar = n * n;
        while(num <= tar){ 
            for(int i = l; i <= r; i++) mat[t][i] = num++; // left to right.
            t++;
            for(int i = t; i <= b; i++) mat[i][r] = num++; // top to bottom.
            r--;
            for(int i = r; i >= l; i--) mat[b][i] = num++; // right to left.
            b--;
            for(int i = b; i >= t; i--) mat[i][l] = num++; // bottom to top.
            l++;
        }
        return mat;
    }
}