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。
示例 1:
输入:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 3
输出: true
示例 2:
输入:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 13
输出: false
代码
// Two binary search
class Solution {
public:
bool searchMatrix(vector<vector<int> > &matrix, int target) {
if (matrix.empty() || matrix[0].empty()) return false;
if (target < matrix[0][0] || target > matrix.back().back()) return false;
int left = 0, right = matrix.size() - 1;
while (left <= right) {
int mid = (left + right) / 2;
if (matrix[mid][0] == target) return true;
else if (matrix[mid][0] < target) left = mid + 1;
else right = mid - 1;
}
int tmp = right;
left = 0;
right = matrix[tmp].size() - 1;
while (left <= right) {
int mid = (left + right) / 2;
if (matrix[tmp][mid] == target) return true;
else if (matrix[tmp][mid] < target) left = mid + 1;
else right = mid - 1;
}
return false;
}
};
