题目描述:
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
.
从右上角row=0,col=cols-1开始查找target元素,如果matrix[row][col]=target返回true,如果matrix[row][col]>target,则令col--;如果matrix[row][col]<target,则令row++
AC代码如下:
class Solution {
public:
bool searchMatrix(vector<vector<int>>& matrix, int target) {
int rows = matrix.size();
if (rows == 0 || matrix[0].size() == 0) return false;
int cols = matrix[0].size();
int row = 0;
int col = cols - 1;
while (row < rows && col >= 0){
int cur_num = matrix[row][col];
if (cur_num == target) return true;
else if (cur_num > target) col--;
else row++;
}
return false;
}
};