[LeetCode] 59. Spiral Matrix II

轉自LeetCode

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 ]
]

<Solution>

Spiral Matrix 的衍生題

這次是倒過來，將 1 到 n^2 的數，用螺旋的順序填到 n x n 的二維矩陣

既然題目是倒過來要求，其時解法也只有一行需要倒過來思考就好

之前是把二維陣列的值拿出來，現在就是把值塞回去二維陣列

其餘都是一樣

code 如下

	class Solution {
	public:
	vector<vector<int>> generateMatrix(int n) {
	if(n <= 0) {
	return vector<vector<int>>();
	}
	vector<vector<int>> ans(n, vector<int>(n, -1));
	const int total = n * n;
	int cnt = 1, moveD = 0;
	int r = 0, c = 0;
	int rowUp = 0, rowDown = n;
	int colLeft = -1, colRight = n;
	while(cnt <= total) {
	ans[r][c] = cnt++; //> put back to n x n array
	switch(moveD) {
	case 0: //> go right
	if(++c == colRight) {
	++r;
	--colRight;
	c = colRight;
	moveD = 1;
	}
	break;
	case 1: //> go down
	if(++r == rowDown) {
	--c;
	--rowDown;
	r = rowDown;
	moveD = 2;
	}
	break;
	case 2: //> go left
	if(--c == colLeft) {
	--r;
	++colLeft;
	c = colLeft;
	moveD = 3;
	}
	break;
	case 3: //> go up
	if(--r == rowUp) {
	++c;
	++rowUp;
	r = rowUp;
	moveD = 0;
	}
	break;
	}
	}
	return ans;
	}
	};

view raw generateSpiralMatrix.cpp hosted with ❤ by GitHub