leetcode59. Spiral Matrix II

59. Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,Given n = 3,You should return the following matrix:[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ]]

解法

同leetcode54. Spiral Matrix，维护四个指针。

public class Solution {    public int[][] generateMatrix(int n) {        // Declaration        int[][] matrix = new int[n][n];        // Edge Case        if (n == 0) {            return matrix;        }        // Normal Case        int rowBegin = 0;        int rowEnd = n - 1;        int colBegin = 0;        int colEnd = n - 1;        int num = 1; //change        while (rowBegin <= rowEnd && colBegin <= colEnd) {            for (int i = colBegin; i <= colEnd; i++) {                matrix[rowBegin][i] = num++; //change            }            rowBegin++;            for (int i = rowBegin; i <= rowEnd; i++) {                matrix[i][colEnd] = num++; //change            }            colEnd--;            for (int i = colEnd; i >= colBegin; i--) {                if (rowBegin <= rowEnd)                    matrix[rowEnd][i] = num++; //change            }            rowEnd--;            for (int i = rowEnd; i >= rowBegin; i--) {                if (colBegin <= colEnd)                    matrix[i][colBegin] = num++; //change            }            colBegin++;        }        return matrix;    }}