编写一个高效的算法来判断 m x n 矩阵中，是否存在一个目标值。该矩阵具有如下特性：
每行中的整数从左到右按升序排列。
每行的第一个整数大于前一行的最后一个整数。
输入：matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 3
输出：true
class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
int result = binarySearch(matrix, target);
if (result == -1) {
return false;
} else {
return binarySearch(matrix[result], target);
}
}
public int binarySearch(int[][] matrix, int target) {
int n = matrix.length;
int left = -1;
int right = n - 1;
while (left < right) {
int mid = left + (right - left + 1) / 2;
if (matrix[mid][0] <= target) {
left = mid;
} else {
right = mid - 1;
}
}
return left;
}
public boolean binarySearch(int[] matrix, int target) {
int n = matrix.length;
int left = 0;
int right = n - 1;
while (left <= right) {
int mid = left + (right - left) / 2;
if (matrix[mid] == target) {
return true;
} else if (matrix[mid] < target) {
left = mid + 1;
} else {
right = mid - 1;
}
}
return false;
}
}