用stl的binary_search寫Search a 2D Matrix

不得不說STL太好用了，二分查找以後也不用自己寫了，雖然二分查找很好寫。。。

題目：

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 from left to right.
• The first integer of each row is greater than the last integer of the previous row.

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, return true.

用stl的binary_search的代碼：

class Solution {
public:
    bool searchMatrix(vector<vector<int> > &matrix, int target) {
        int n = matrix.size();
        if(n == 0) return false;
        int m = matrix[0].size();
        for(int i=0; i<n; i++) {
            if(matrix[i][0] <= target && matrix[i][m-1] >= target) {
                if(binary_search(matrix[i].begin(), matrix[i].end(), target)) {
                    return true;
                }
            }
        }
        return false;
    }
};