interviews/leetcode/array/SpiralMatrixII.java at master · codingOnGithub/interviews · GitHub

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// 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 ]

// ]

public class SpiralMatrix {

public int[][] generateMatrix(int n) {

int[][] spiral = new int[n][n];

if(n == 0) {

return spiral;

}

int rowStart = 0;

int colStart = 0;

int rowEnd = n - 1;

int colEnd = n -1;

int number = 1;

while(rowStart <= rowEnd && colStart <= colEnd) {

for(int i = colStart; i <= colEnd; i++) {

spiral[rowStart][i] = number++;

}

rowStart++;

for(int i = rowStart; i <= rowEnd; i++) {

spiral[i][colEnd] = number++;

}

colEnd--;

for(int i = colEnd; i >= colStart; i--) {

if(rowStart <= rowEnd) {

spiral[rowEnd][i] = number++;

}

rowEnd--;

for(int i = rowEnd; i >= rowStart; i--) {

if(colStart <= colEnd) {

spiral[i][colStart] = number++;

}

colStart++;

}

return spiral;

}

interviews/leetcode/array/SpiralMatrixII.java at master · codingOnGithub/interviews · GitHub

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