Search a 2D Matrix
27% Accepted
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.
Consider the following matrix:
[
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
Given target = 3, return true.
Challenge
O(log(n) + log(m)) time
Tags Expand
- Binary Search
- Matrix
思路
- 两次二分搜索
public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
return false;
}
int m = matrix.length;
int n = matrix[0].length;
int start = 0;
int end = m - 1;
while (start < end - 1) {
int mid = start + (end - start) / 2;
if (matrix[mid][0] == target) {
return true;
}
else if (matrix[mid][0] > target) {
end = mid;
}
else {
start = mid;
}
}
int row = (matrix[end][0] <= target) ? end : start;
start = 0;
end = n - 1;
while (start < end - 1) {
int mid = start + (end - start) / 2;
if (matrix[row][mid] == target) {
return true;
}
else if (matrix[row][mid] > target) {
end = mid;
}
else {
start = mid;
}
}
return (matrix[row][start] == target || matrix[row][end] == target);
}
}