要考虑边界，刚开始没判断，结果没通过；再就是考虑进入行的判断，如果超出边界就直接下一行。
class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
if (matrix.length == 0 || matrix[0].length == 0) return false;
for(int[] row : matrix) {
int left = 0, right = row.length - 1;
if (row[left] > target || target > row[right])
continue;
while (left <= right) {
int mid = (left + right) / 2;
if (row[mid] == target) return true;
if (target < row[mid])
right = mid - 1;
else
left = mid + 1;
}
}
return false;
}
}