題目描述

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, returntrue.

有序二維矩陣找數，先確定範圍再二分查找

 1 class Solution {
 2 public:
 3     bool searchMatrix(vector<vector<int> > &matrix, int target) {
 4         int m=matrix.size(),n=matrix[0].size();
 5         int i=0;
 6
 
         for(i=0;i<m;i++){
 7             if(target>=matrix[i][0]&&target<=matrix[i][n-1])
 8                 break;
 9         }
10         if(i==m) return false;
11         int left=0,right=n-1;
12         while(left<=right){
13             int mid=(left+right)/2;
14             if(target==matrix[i][left]||target==matrix[i][right]||target==matrix[i][mid])
 
15                 return true;
16             if(target<matrix[i][mid])
17                 right=mid-1;
18             else
19                 left=mid+1;
20         }
21         return false;
22     }
23 };

search-a-2d-matrix——二維矩陣找數