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59. 螺旋矩阵 II

Introduction

Question: 59. 螺旋矩阵 II

给你一个正整数 n ，生成一个包含 1 到 n2 所有元素，且元素按顺时针顺序螺旋排列的 n x n 正方形矩阵 matrix 。

 

示例 1：

输入：n = 3
输出：1,2,3],[8,9,4],[7,6,5

示例 2：

输入：n = 1
输出：1

 

提示：

  • 1 <= n <="20

解法一

Analysis

和LC54-spiral-matrix非常类似，直接改改之前代码就过了。

Implement

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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<vector<int>> generateMatrix(int n) {
    vector<vector<int>> res(n, vector<int>(n));

    ifirst = jfirst = 0;
    ilast = jlast = n-1;
    int i = 0, j = 0, state = 0;
    ifirst++;

    for(int t = 1, size = n*n;t <= size;t++) {
        res[i][j] = t;
        transform(i, j, state);
    }

    return res;
}