题解 | #寻找牛群中的特定编号牛#

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param matrix int整型vector<vector<>> 
     * @param target int整型 
     * @return bool布尔型
     */
    bool searchMatrix(vector<vector<int> >& matrix, int target) {
        // write code here
        // 二分查找
        int low_row = 0;
        int high_row = matrix.size()-1; 
        while(low_row < high_row)
        {
            // 不能简单写成int mid = (low_row + high_row)>>1 ；否则会陷入死循环
            int mid = low_row + (low_row+high_row) >> 1;
            if(matrix[mid][0] < target)
                high_row = mid-1;
            else
                low_row = mid;
        }

        int left = 0;
        int right = matrix[0].size()-1;
        while(left < right)
        {
            int mid = (left+right) >> 1;
            if(matrix[low_row][mid]==target)
                return true;
            else if(matrix[low_row][mid] > target)
                left = mid+1;
            else
                right = mid-1;
        }

        return matrix[low_row][left] == target ? true : false;
    }
};