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.

Solution:

从右上角开始找起。time complexcity是O(M+N)

    bool searchMatrix(vector<vector > &matrix, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(matrix.size()==0||matrix[0].size()==0)
            return false;

        int col = matrix[0].size()-1;
        int row = 0;

        while(row<matrix.size()&&col>=0)
        { 
            if(target==matrix[row][col])
                    return true;
            else if(target>matrix[row][col])//go down
                    row++;
            else//go left
                    col--;
        }

        return false;        
    }
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