leetcode 90: Search a 2D Matrix

Search a 2D MatrixApr
7 '12

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

.

public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
// Start typing your Java solution below
// DO NOT write main() function

//check input;
if(matrix==null || matrix[0]==null) return false;

int m = matrix.length;
int n = matrix[0].length;

int low = 0;
int high = m*n-1;

while(low<=high) {
int mid = low + (high-low)/2;

int mvalue = matrix[mid/n][mid%n];

if(mvalue == target) return true;
else if(mvalue < target) {
low = mid + 1;
} else {
high = mid - 1;
}
}
return false;
}
}

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 n = matrix.size();
if(n==0) return false;
int m = matrix[0].size();
int len = n*m;

int low = 0;
int high = len-1;

while(low<=high) {
int mid = low + (high - low) / 2;
int midx = mid / m;
int midy = mid % m;
int midval = matrix[midx][midy];

if(midval == target) return true;
else if(target < midval) {
high = mid - 1;
} else {
low = mid + 1;
}
}
return false;
}
};