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

 class Solution {
 public:
     bool searchMatrix(vector<vector<int> > &matrix, int target) {
         int m=matrix.size(),n=matrix[].size();
         int i=;
         for(i=;i<m;i++){
             if(target>=matrix[i][]&&target<=matrix[i][n-])
                 break;
         }
         if(i==m) return false;
         int left=,right=n-;
         while(left<=right){
             int mid=(left+right)/;
             if(target==matrix[i][left]||target==matrix[i][right]||target==matrix[i][mid])
                 return true;
             if(target<matrix[i][mid])
                 right=mid-;
             else
                 left=mid+;
         }
         return false;
     }
 };