[LeetCode-74] Search a 2D Matrix

Search a 2D Matrix

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.

 

水题

 

class Solution {
    public:
        bool searchMatrix(vector<vector<int> > &matrix, int target) {
            // Start typing your C/C++ solution below
            // DO NOT write int main() function 
            int row_cnt = matrix.size();
            if (0 == row_cnt) {
                return false;
            }
            int col_cnt = matrix.at(0).size();
            if (target > matrix.at(row_cnt - 1).at(col_cnt - 1)) {
                return false;
            }

            vector<int> row_max;
            for (vector<vector<int> >::iterator iter = matrix.begin();
                    iter != matrix.end(); ++iter) {
                row_max.push_back(iter->at(col_cnt - 1));
            }   
            int target_row = std::lower_bound(row_max.begin(), row_max.end(), target) - row_max.begin();
            return std::binary_search(matrix.at(target_row).begin(), 
                    matrix.at(target_row).end(), target);
                    
        }
};