54. 螺旋矩阵

Introduction

Question：54. 螺旋矩阵

Analysis

要实现回行遍历（注意不是螺旋）只需要用一个state来标识行动方向，然后通过判断是否到达边界来更新方向即可。

而螺旋遍历的话，还需要用而外的4个值来分别控制横向、纵向的边界。在每次切换边界时更新对应的边界。

Implement

int ifirst, ilast, jfirst, jlast;
vector<int> moveI{0, 1, 0, -1};
vector<int> moveJ{1, 0, -1, 0};
void transform(int &i, int &j, int &state) {
    if (state == 0 && j == jlast) {
        state = (state + 1) % 4;
        jlast--;
    } else if (state == 1 && i == ilast) {
        state = (state + 1) % 4;
        ilast--;
    } else if (state == 2 && j == jfirst) {
        state = (state + 1) % 4;
        jfirst++;
    } else if (state == 3 && i == ifirst) {
        state = (state + 1) % 4;
        ifirst++;
    }
    i += moveI[state];
    j += moveJ[state];
}
vector<int> spiralOrder(vector<vector<int>>& matrix) {
    int m = matrix.size();
    if (m == 0) return vector<int>();
    int n = matrix[0].size();
    vector<int> res(m*n);
    int i = 0, j = 0;
    ifirst = jfirst = 0;
    ilast = m - 1;
    jlast = n - 1;
    ifirst++;

    int state = 0;

    for(int index = 0, size = m*n; index < size; index++) {
        res[index] = matrix[i][j];
        transform(i, j, state);     
    }
    return res;
}