LeetCode Search a 2D Matrix

// 68ms  size 返回的是无符号整数，和负数比较时序特别注意转换
 1 class Solution {
public:
    bool searchMatrix(vector<vector<int> > &matrix, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int i=-1;
        for(;i<(int)(matrix.size()-1);i++)
        {
            if(target<matrix[i+1][0])
                break;
        }
        if(i==-1)
        {
            return false;
        }
        vector<int>::iterator p;
        p=find(matrix[i].begin(),matrix[i].end(),target);
        if(p!=matrix[i].end())
            return true;
        else
            return false;
    }
};