矩阵

package top100.top矩阵;import java.util.ArrayList;
import java.util.List;public class TOP {//73. 矩阵置零//额外空间将有0的行列存储下来，再置0public void setZeroes(int[][] matrix) {int m = matrix.length;int n = matrix[0].length;boolean[] row = new boolean[m];boolean[] col = new boolean[n];for (int i = 0; i < m; i++) {for (int j = 0; j < n; j++) {if (matrix[i][j] == 0) {row[i] = col[j] = true;}}}for (int i = 0; i < m; i++) {for (int j = 0; j < n; j++) {if (row[i] || col[j]) {matrix[i][j] = 0;}}}}//54. 螺旋矩阵//直接转圈遍历，每遍历行或列，就修改行列的索引public List<Integer> spiralOrder(int[][] matrix) {List<Integer> res = new ArrayList<>();int m = matrix.length, n = matrix[0].length;int top = 0, bottom = m - 1, left = 0, right = n - 1; //定义四个边界，遍历完边界，更新边界int count = m * n; //元素个数while (count > 0) {//遍历top行for (int i = left; i <= right && count > 0; i++) {res.add(matrix[top][i]);count--;}top++;//遍历right列for (int i = top; i <= bottom && count > 0; i++) {res.add(matrix[i][right]);count--;}right--;//遍历bottom行for (int i = right; i >= left && count > 0; i--) {res.add(matrix[bottom][i]);count--;}bottom--;//遍历left列for (int i = bottom; i >= top && count > 0; i--) {res.add(matrix[i][left]);count--;}left++;}return res;}//48. 旋转图像//只能靠找规律了//先上下交换，再对角线交换public void rotate(int[][] matrix) {int n = matrix.length;//上下交换for (int i = 0; i < n / 2; i++) {for (int j = 0; j < n; j++) {int v = matrix[n - i - 1][j];matrix[n - i - 1][j] = matrix[i][j];matrix[i][j] = v;}}//对角线交换for (int i = 0; i < n; i++) {for (int j = i + 1; j < n; j++) {int v = matrix[i][j];matrix[i][j] = matrix[j][i];matrix[j][i] = v;}}}//240. 搜索二维矩阵 II//一看到搜索和排序，就联想到2分法public boolean searchMatrix(int[][] matrix, int target) {int m = matrix.length, n = matrix[0].length;int i = m - 1, j = 0; //从左下角开始搜索while (i >= 0 && j < n) {if (matrix[i][j] > target) {i--;} else if (matrix[i][j] < target) {j++;} else {return true;}}return false;}
}