矩阵处理技巧

核心技巧:找到coding上的宏观调度

zigzag打印矩阵

public class ZigZagPrintMatrix {

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

	public static void printLevel(int[][] m, int tR, int tC, int dR, int dC,
			boolean f) {
		if (f) {
			while (tR != dR + 1) {
				System.out.print(m[tR++][tC--] + " ");
			}
		} else {
			while (dR != tR - 1) {
				System.out.print(m[dR--][dC++] + " ");
			}
		}
	}

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

转圈打印矩阵

public class 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 a, int b, int c, int d) {
		if (a == c) {
			for (int i = b; i <= d; i++) {
				System.out.print(m[a][i] + " ");
			}
		} else if (b == d) {
			for (int i = a; i <= c; i++) {
				System.out.print(m[i][b] + " ");
			}
		} else {
			int curC = b;
			int curR = a;
			while (curC != d) {
				System.out.print(m[a][curC] + " ");
				curC++;
			}
			while (curR != c) {
				System.out.print(m[curR][d] + " ");
				curR++;
			}
			while (curC != b) {                                                                             
				System.out.print(m[c][curC] + " ");
				curC--;
			}
			while (curR != a) {
				System.out.print(m[curR][b] + " ");
				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);
	}
}

原地旋转正方形矩阵

public class RotateMatrix {

	public static void rotate(int[][] matrix) {
		int a = 0;
		int b = 0;
		int c = matrix.length - 1;
		int d = matrix[0].length - 1;
		while (a < c) {
			rotateEdge(matrix, a++, b++, c--, d--);
		}
	}

	public static void rotateEdge(int[][] m, int a, int b, int c, int d) {
		int tmp = 0;
		for (int i = 0; i < d - b; i++) {
			tmp = m[a][b + i];
			m[a][b + i] = m[c - i][b];
			m[c - i][b] = m[c][d - i];
			m[c][d - i] = m[a + i][d];
			m[a + i][d] = 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);
	}
}