Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:
- Integers in each row are sorted in ascending from left to right.
- Integers in each column are sorted in ascending from top to bottom.
For example,
Consider the following matrix:
[ [1, 4, 7, 11, 15], [2, 5, 8, 12, 19], [3, 6, 9, 16, 22], [10, 13, 14, 17, 24], [18, 21, 23, 26, 30] ]
Given target = 5, return true.
Given target = 20, return false.
题目含义：矩阵的行和列都是升序排列，查找一个数是否在矩阵中
1 public boolean searchMatrix(int[][] matrix, int target) { 2 // 从右上角开始, 比较target 和 matrix[i][j]的值. 先列后行来逼近。如果大于target, 则该列不可能有此数, 所以j--。如果小于target, 则该行不可能有此数, 所以i++; 4 if (matrix.length == 0 || matrix[0].length == 0) return false; 5 int i = 0, j = matrix[0].length - 1; 6 while (i < matrix.length && j >= 0) { 7 int x = matrix[i][j]; 8 if (target == x) return true; 9 else if (target < x) j--; 10 else i++; 11 } 12 return false; 13 }