leetcode[74]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.

class Solution {

public:

    bool searchMatrix(vector<vector<int> > &matrix, int target) {

        if(matrix.empty())return false;

        int row=matrix.size();

        if(matrix[0].empty())return false;

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

        int left=0,right=row*col-1;

        while(left<=right)

        {

            int mid=(left+right)/2;

            int temp=matrix[mid/col][mid%col];

            if(temp==target)return true;

            else if(temp<target)left=mid+1;

            else right=mid-1;

        }

        return false;

    }

/**

    bool searchMatrix(vector<vector<int> > &matrix, int target) {

        if(matrix.empty())return false;

        int row=matrix.size();

        if(matrix[0].empty())return false;

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

        int i=0,j=col-1;

        while(i<row&&j>=0)

        {

            if(matrix[i][j]==target)return true;

            else if(matrix[i][j]<target)i++;

            else j--;

        }

        return false;

    }

*/

};