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  • [leetcode]Search a 2D Matrix

    Search a 2D Matrix

    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.

    算法思路:

    本题肯定要用二分查找的,如果是一维数组就完美了,可惜是二维,不过没关系,可以将二维数组抽象成一维。继续按照一维来操作。

    代码如下:

     1 public class Solution {
     2     public boolean searchMatrix(int[][] matrix, int target) {
     3         if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return false;
     4         int height = matrix.length;
     5         int width = matrix[0].length;
     6         int begin = 0, end = height * width - 1;
     7         while(begin <= end){
     8             int mid = (begin + end) >> 1;
     9             int i = mid / width;
    10             int j = mid % width;
    11             if(matrix[i][j] == target){
    12                 return true;
    13             }else if(matrix[i][j] < target){
    14                 begin = mid + 1;
    15             }else{
    16                 end = mid - 1;
    17             }
    18         }
    19         return false;        
    20     }
    21 }
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  • 原文地址:https://www.cnblogs.com/huntfor/p/3905526.html
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