2014
11-18

# LeetCode-Search a 2D Matrix[查找]

### 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.

// LeetCode, Search a 2D Matrix
// 时间复杂度O(logn)，空间复杂度O(1)
class Solution {
public:
bool searchMatrix(const vector<vector<int>>& matrix, int target) {
if (matrix.empty()) return false;
const size_t  m = matrix.size();
const size_t n = matrix.front().size();

int first = 0;
int last = m * n;

while (first < last) {
int mid = first + (last - first) / 2;
int value = matrix[mid / n][mid % n];

if (value == target)
return true;
else if (value < target)
first = mid + 1;
else
last = mid;
}

return false;
}
};


Java代码:

public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
int row=0;
int m = matrix.length;
int n = matrix[0].length;
int col=n-1;
while(row < m && col >= 0){
if(matrix[row][col] == target)
return true;
else if(matrix[row][col] < target)
row++;
else col--;
}
return false;
}
}

1. 算法是程序的灵魂，算法分简单和复杂，如果不搞大数据类，程序员了解一下简单点的算法也是可以的，但是会算法的一定要会编程才行，程序员不一定要会算法，利于自己项目需要的可以简单了解。