矩阵“回”，“之”，翻转打印

1. ‘回’字型打印

     思路：从最外回字往里面一层层打印。如：

                                                         

代码如下：

package class_03;

public class Code_06_PrintMatrixSpiralOrder {

	public static void spiralOrderPrint(int[][] matrix) {
		int tR = 0;
		int tC = 0;
		int dR = matrix.length - 1;
		int dC = matrix[0].length - 1;
		while (tR <= dR && tC <= dC) {
			printEdge(matrix, tR++, tC++, dR--, dC--);
		}
	}

	public static void printEdge(int[][] m, int tR, int tC, int dR, int dC) {
		if (tR == dR) {
			for (int i = tC; i <= dC; i++) {
				System.out.print(m[tR][i] + " ");
			}
		} else if (tC == dC) {
			for (int i = tR; i <= dR; i++) {
				System.out.print(m[i][tC] + " ");
			}
		} else {
			int curC = tC;
			int curR = tR;
			while (curC != dC) {
				System.out.print(m[tR][curC] + " ");
				curC++;
			}
			while (curR != dR) {
				System.out.print(m[curR][dC] + " ");
				curR++;
			}
			while (curC != tC) {
				System.out.print(m[dR][curC] + " ");
				curC--;
			}
			while (curR != tR) {
				System.out.print(m[curR][tC] + " ");
				curR--;
			}
		}
	}

	public static void main(String[] args) {
		int[][] matrix = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 },
				{ 13, 14, 15, 16 } };
		spiralOrderPrint(matrix);

	}

}

2. ‘之’ 字型打印

    思路：设置两个对应点A和B，都从（0,0）位置开始。A往右边走，B往下边走，A，B同时运动，以此形成对角线（打印对角线上的数就可以了，轮着交换从A or B开始打）。A如果走到了最右边，就往下走。B如果走到了最下边，就往右走。如：

                                                                             

代码如下：

package class_03;

public class Code_08_ZigZagPrintMatrix {

	public static void printMatrixZigZag(int[][] matrix) {
		int aR = 0;
		int aC = 0;
		int bR = 0;
		int bC = 0;
		int endR = matrix.length - 1;
		int endC = matrix[0].length - 1;
		boolean fromUp = false;
		while (aR != endR + 1) {  
			printLevel(matrix, aR, aC, bR, bC, fromUp);
			aR = aC == endC ? aR + 1 : aR;
			aC = aC == endC ? aC : aC + 1;
			bC = bR == endR ? bC + 1 : bC;
			bR = bR == endR ? bR : bR + 1;
			fromUp = !fromUp;
		}
		System.out.println();
	}

	public static void printLevel(int[][] m, int aR, int aC, int bR, int bC,
			boolean f) {
		if (f) { // 从a往b打印
			while (aR != bR + 1) {
				System.out.print(m[aR++][aC--] + " ");
			}
		} else {  // 从b往a打印
			while (bR != aR - 1) {
				System.out.print(m[bR--][bC++] + " ");
			}
		}
	}

	public static void main(String[] args) {
		int[][] matrix = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 } };
		printMatrixZigZag(matrix);

	}

}

3. 顺时针翻转正方形90度

     思路：按照上面打印‘回’字的思想，一层层下去，每一层都交换四边的所对应的值。

package class_03;

public class Code_05_RotateMatrix {

	public static void rotate(int[][] matrix) {
		int tR = 0;
		int tC = 0;
		int dR = matrix.length - 1;
		int dC = matrix[0].length - 1;
		while (tR < dR) {      // 从最外往里打印
			rotateEdge(matrix, tR++, tC++, dR--, dC--);
		}
	}

	public static void rotateEdge(int[][] m, int tR, int tC, int dR, int dC) {
		int times = dC - tC; 
		int tmp = 0;
		for (int i = 0; i != times; i++) {   //交换四条边上对应的点
			tmp = m[tR][tC + i];
			m[tR][tC + i] = m[dR - i][tC];
			m[dR - i][tC] = m[dR][dC - i];
			m[dR][dC - i] = m[tR + i][dC];
			m[tR + i][dC] = tmp;
		}
	}

	public static void printMatrix(int[][] matrix) {
		for (int i = 0; i != matrix.length; i++) {
			for (int j = 0; j != matrix[0].length; j++) {
				System.out.print(matrix[i][j] + " ");
			}
			System.out.println();
		}
	}

	public static void main(String[] args) {
		int[][] matrix = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 },
				{ 13, 14, 15, 16 } };
		printMatrix(matrix);
		rotate(matrix);
		System.out.println("=========");
		printMatrix(matrix);
	}

}