[leetcode] 【查找】 74. 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.

题意

判断一个矩阵中是否包含目标元素，矩阵有两个特性：从左到右排序；每一行第一个元素比上一行最后一个元素大。

题解

使用二分法，把矩阵看成是一维数据处理。   长度为col*raw          用的时候下标为    mid/row   mid%row  

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        if(matrix.empty()) return false;
        const size_t high=matrix.size();
        const size_t len=matrix[0].size();
        int begin=0,end=high*len-1,mid=0;
        while(begin<end)
        {
            mid=(begin+end)/2;
            int val=matrix[mid/len][mid%len];
            if(val==target) return true;
            if(val>target) end=mid;
            else begin=mid+1;
        }
        if(matrix[begin/len][begin%len]==target ) return true;
        return false;
    }
};