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.

C++实现代码如下：

#include<iostream>

#include<vector>

using namespace std;



class Solution

{

public:

    bool searchMatrix(vector<vector<int> > &matrix, int target)

    {

        if(matrix.empty()||matrix[0].empty())

            return false;

        int i=0;

        int j=matrix[0].size()-1;

        int temp;

        while(i<(int)matrix.size()&&j>=0)

        {

            temp=matrix[i][j];

            if(target==temp)

                return true;

            else if(target<temp)

                j--;

            else if(target>temp)

                i++;

        }

        return false;

    }

};



int main()

{

    Solution s;

    vector<vector<int> > vec=

    {

        {-10,-9},

        {-7,-6},

        {-5,-4},

        {-3,-2}

    };

    cout<<s.searchMatrix(vec,-6)<<endl;

}

开始提交了一种，死活通不过。

class Solution {

public:

    bool searchMatrix(vector<vector<int> > &matrix, int target) {

        if(matrix.empty()||matrix[0].empty())

            return false;

        size_t i=0;

        size_t j=matrix[0].size()-1;

        int temp;

        while(i<matrix.size()&&j>=0)

        {

            temp=matrix[i][j];

            if(target==temp)

                return true;

            if(target<temp)

            {

                j--;

                continue;

            }

            if(target>temp)

            {

                i++;

                continue;

            }

        }

        if(i>=matrix.size()||j<0)

            return false;

        return true;

    }

};

一直报错Last executed input:[[-10],[-7],[-4]], -6

就因为将i和j声明为size_t类型，可能出现下溢。可以参考：https://oj.leetcode.com/discuss/11366/why-is-the-last-executed-input-error