search-a-2d-matrix——二维矩阵找数

题目描述

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.

有序二维矩阵找数，先确定范围再二分查找

 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 };