题目
编写一个高效的算法来搜索 m x n 矩阵 matrix 中的一个目标值 target 。该矩阵具有以下特性: 每行的元素从左到右升序排列。 每列的元素从上到下升序排列。
示例 1:
输入: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]]
, target = 5
输出:true
示例 2:
输入: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]]
, target = 20
输出:false
提示:
m == matrix.length
n == matrix[i].length
1 <= n, m <= 300
-109 <= matix[i][j] <= 109
每行的所有元素从左到右升序排列
每列的所有元素从上到下升序排列
-109 <= target <= 109
解法
一遍横着找,一边列着找 => 缩小问题的规模;
class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
if (matrix == null || matrix.length == 0) {
throw new RuntimeException("illegle input params");
}
int rowBegin = 0;
int rowEnd = matrix.length - 1;
int colBegin = 0;
int colEnd = matrix[0].length - 1;
while (colEnd >= colBegin && rowBegin <= rowEnd) {
int mid = matrix[rowBegin][colEnd];
if (mid == target) {
return true;
} else if (target > mid) {
rowBegin++;
} else if (target < mid) {
colEnd--;
}
}
return false;
}
}