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.

 

二分查找，时间复杂度O(logm)+O(logn)。

1 class Solution { 2 public: 3     bool searchMatrix(vector
     
      
       >& matrix, int target) { 4         if(matrix.size()==0 || matrix[0].size()==0) return false; 5         int m=matrix.size(),n=matrix[0].size(); 6         int left=0,right=m-1; 7         while(left<=right) 8         { 9             int mid = (left+right)/2;10             if(matrix[mid][0]==target) return true;11             else if(matrix[mid][0]
      
     

 

这题也可以从右上角遍历，时间复杂度O(m)+O(n)。

1 class Solution { 2 public: 3     bool searchMatrix(vector
     
      
       >& matrix, int target) { 4         if(matrix.size()==0 || matrix[0].size()==0) return false; 5         int m=matrix.size(),n=matrix[0].size(); 6         int row=0,col=n-1; 7         while(row
       
        =0) 8         { 9             if(matrix[row][col]==target) return true;10             else if(matrix[row][col]