Arrays_Strings 把一个矩阵置为0 @CareerCup-优快云博客

本文介绍了一种在矩阵中快速定位并替换零元素的方法，通过仅使用额外的两个布尔数组来存储行和列是否包含零元素，从而避免了传统方法中逐元素检查的高时间复杂度。

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LeetCode 原题：http://blog.youkuaiyun.com/fightforyourdream/article/details/14220585

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package Arrays_Strings;

import CtCILibrary.AssortedMethods;

public class S1_7 {

	public static void nullifyRow(int[][] matrix, int row) {
		for (int j = 0; j < matrix[0].length; j++) {
			matrix[row][j] = 0;
		}		
	}

	public static void nullifyColumn(int[][] matrix, int col) {
		for (int i = 0; i < matrix.length; i++) {
			matrix[i][col] = 0;
		}		
	}		

	public static void setZeros2(int[][] matrix) {
		boolean rowHasZero = false;
		boolean colHasZero = false;		

		// Check if first row has a zero
		for (int j = 0; j < matrix[0].length; j++) {
			if (matrix[0][j] == 0) {
				rowHasZero = true;
				break;
			}
		}		

		// Check if first column has a zero
		for (int i = 0; i < matrix.length; i++) {
			if (matrix[i][0] == 0) {
				colHasZero = true;
				break;
			}
		}		

		// Check for zeros in the rest of the array
		for (int i = 1; i < matrix.length; i++) {
			for (int j = 1; j < matrix[0].length;j++) {
				if (matrix[i][j] == 0) {
					matrix[i][0] = 0;
					matrix[0][j] = 0;
		 		}
			}
		}		

		// Nullify rows based on values in first column
		for (int i = 1; i < matrix.length; i++) {
			if (matrix[i][0] == 0) {
				nullifyRow(matrix, i);
			}
		}		

		// Nullify columns based on values in first row
		for (int j = 1; j < matrix[0].length; j++) {
			if (matrix[0][j] == 0) {
				nullifyColumn(matrix, j);
			}
		}	

		// Nullify first row
		if (rowHasZero) {
			nullifyRow(matrix, 0);
		}

		// Nullify first column
		if (colHasZero) {
			nullifyColumn(matrix, 0);
		}
	}	

	public static void setZeros(int[][] matrix) {
		boolean[] row = new boolean[matrix.length];	
		boolean[] column = new boolean[matrix[0].length];

		// Store the row and column index with value 0
		for (int i = 0; i < matrix.length; i++) {
			for (int j = 0; j < matrix[0].length;j++) {
				if (matrix[i][j] == 0) {
					row[i] = true; 
					column[j] = true;
		 		}
			}
		}

		// Nullify rows
		for (int i = 0; i < row.length; i++) {
			if (row[i]) {
				nullifyRow(matrix, i);
			}
		}

		// Nullify columns
		for (int j = 0; j < column.length; j++) {
			if (column[j]) {
				nullifyColumn(matrix, j);
			}
		}
	}	

	public static boolean matricesAreEqual(int[][] m1, int[][] m2) {
		if (m1.length != m2.length || m1[0].length != m2[0].length) {
			return false;
		}

		for (int k = 0; k < m1.length; k++) {
			for (int j = 0; j < m1[0].length; j++) {
				if (m1[k][j] != m2[k][j]) {
					return false;
				}
			}
		}	
		return true;
	}

	public static int[][] cloneMatrix(int[][] matrix) {
		int[][] c = new int[matrix.length][matrix[0].length];
		for (int i = 0; i < matrix.length; i++) {
			for (int j = 0; j < matrix[0].length; j++) {
				c[i][j] = matrix[i][j];
			}
		}
		return c;
	}

	public static void main(String[] args) {
		int nrows = 10;
		int ncols = 15;
		int[][] matrix1 = AssortedMethods.randomMatrix(nrows, ncols, 0, 100);		
		int[][] matrix2 = cloneMatrix(matrix1);

		AssortedMethods.printMatrix(matrix1);

		setZeros(matrix1);
		setZeros2(matrix2);

		System.out.println();

		AssortedMethods.printMatrix(matrix1);
		System.out.println();
		AssortedMethods.printMatrix(matrix2);

		if (matricesAreEqual(matrix1, matrix2)) {
			System.out.println("Equal");
		} else {
			System.out.println("Not Equal");
		}
	}
}