Spiral Matrix II

最新推荐文章于 2025-01-09 18:09:55 发布

yangmicheal

最新推荐文章于 2025-01-09 18:09:55 发布

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分类专栏： leetCode Solutions

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本文介绍了一种生成矩阵的高效算法，通过控制方向和边界条件，实现了从左上角开始填充数字直到整个矩阵被完全填充的过程。此算法利用了switch-case结构来处理四个主要方向的移动，并在遇到边界或已填充的单元格时改变方向。

public class Solution {
    public int[][] generateMatrix(int n) {
        // 0 up, 1 down, 2 left, 3 right
        int val = 1;
        int pre = 3;
        int i = 0;
        int j = 0;
        int[][] m = new int[n][n];
        while(val<=n*n){
            m[i][j] = val++;
            switch (pre){
                case 0:
                    if (i+1<n && m[i+1][j] == 0) {
                        i++;
                    // Cannot go up, turn left.     
                    }else {
                        j--;
                        pre = 2;
                    }
                    break;
                case 1:
                    if (i-1>=0 && m[i-1][j] == 0){
                        i--;
                    // Cannot go down, turn right.  
                    }else{
                        j++;
                        pre = 3;
                    }
                    break;
                case 2:
                    if (j-1>=0 && m[i][j-1] == 0){
                        j--;
                    // Cannot go left, turn down.  
                    }else{
                        i--;
                        pre = 1;
                    }
                    break;
                case 3:
                    if (j+1<n && m[i][j+1] == 0){
                        j++;
                    // Cannot go right, turn up.  
                    }else{
                        i++;
                        pre = 0;
                    }
                    break;
                default: break;    
            }
        }
        return m;
    }
}