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[0].size();
        int i=0;
        for(i=0;i<m;i++){
            if(target>=matrix[i][0]&&target<=matrix[i][n-1])
                break;
        }
        if(i==m) return false;
        int left=0,right=n-1;
        while(left<=right){
            int mid=(left+right)/2;
            if(target==matrix[i][left]||target==matrix[i][right]||target==matrix[i][mid])
                return true;
            if(target<matrix[i][mid])
                right=mid-1;
            else
                left=mid+1;
        }
        return false;
    }
};