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 in ascending from left to right.
- Integers in each column are sorted in ascending from top to bottom.
For example,
Consider the following matrix:
[
[1, 4, 7, 11, 15],
[2, 5, 8, 12, 19],
[3, 6, 9, 16, 22],
[10, 13, 14, 17, 24],
[18, 21, 23, 26, 30]
]
Given target = 5, return true.
Given target = 20, return false.
一刷
题解：因为每一行左<右，每一列，上<下
所以从右上角开始寻找。如果小于target就向下，如果大于target就向左
public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
if(matrix == null || matrix.length==0 || matrix[0].length == 0) return false;
int col = matrix[0].length-1;
int row = 0;
while(col>=0 && row<=matrix.length-1){
if(target == matrix[row][col]) return true;
else if(target<matrix[row][col]) col--;
else row++;
}
return false;
}
}
二刷
同上
public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
if(matrix.length == 0) return false;
int m = matrix.length;
int n = matrix[0].length;
int row = 0, col = n-1;
while(row<m && col>=0){
if(matrix[row][col]>target) col--;
else if(matrix[row][col]<target) row++;
else return true;
}
return false;
}
}
Binary Search
