LintCode 374-螺旋矩阵状态机_lintcode374-优快云博客

本文介绍了一种使用状态机实现的矩阵螺旋遍历算法。通过定义四种状态：左转、右转、上移和下移，并结合已访问标记矩阵来避免重复访问，实现了对二维矩阵的螺旋式遍历。

使用状态机的思路，运用四个状态来回切换，并用count计算步长最终退出。

 static public List<Integer> spiralOrder(int[][] matrix) {
        // Write your code here
        List<Integer> ret = new ArrayList<>();
        if (matrix.length == 0) return ret;


        int i = 0;
        int j = 0;
        int state = 2;
        int maxstep = matrix.length * matrix[0].length;
        int count = 0;
        final int TURNLEFT = 1, TURNRIGHT = 2, TURNUP = 3, TURNDOWM = 4;//定义了四种状态
        int visited[][] = new int[matrix.length][matrix[0].length];//定义一个已走过的矩阵
        while (count < matrix.length * matrix[0].length) {
            int temp = matrix[i][j];


            count++;//每走一次都加一

            switch (state) {

                case TURNLEFT: {
                    ret.add(temp);
                    visited[i][j] = 1;
                    if (j == 0 || visited[i][j - 1] == 1) {
                        i--;
                        state = TURNUP;
                    }
                    else {
                        j--;
                        state = TURNLEFT;
                    }

                    break;
                }
                case TURNRIGHT: {
                    ret.add(temp);
                    visited[i][j] = 1;
                    if (j + 1 == matrix[0].length || visited[i][j + 1] == 1) {
                        state = TURNDOWM;
                        i++;
                    }
                    else {

                        j++;
                        state = TURNRIGHT;
                    }

                    break;
                }
                case TURNUP: {
                    ret.add(temp);
                    visited[i][j] = 1;
                    if (i == 0 || visited[i - 1][j] == 1) {
                        j++;
                        state = TURNRIGHT;
                    }
                    else {
                        i--;
                        state = TURNUP;
                    }

                    break;
                }
                case TURNDOWM: {
                    ret.add(temp);
                    visited[i][j] = 1;
                    if (i + 1 == matrix.length || visited[i + 1][j] == 1) {
                        j--;
                        state = TURNLEFT;
                    }
                    else {
                        i++;
                        state = TURNDOWM;
                    }

                    break;

                }
            }
        }

    return ret;
    }