leetcode--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.

题意：给定一个矩阵。对于每一行，从左到右递增，对应每一列，从上到下递增。求指定target是否在矩阵中

分类：数组，二分法

解法1：target和右上角的元素比较，如果比它大说明在下一行，如果比它小，说明在它的列之前

这样就可以快速划分行列范围

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1. public class Solution {  
2.     public boolean searchMatrix(int[][] matrix, int target) {  
3.         int m = matrix.length;  
4.         int n = matrix[0].length-1;  
5.         int i = 0;  
6.         while(n>=0&&i<m){  
7.             if(matrix[i][n]==target){  
8.                 return true;  
9.             }else if(matrix[i][n]<target){  
10.                 i++;  
11.             }else{  
12.                 n--;  
13.             }  
14.         }  
15.         return false;  
16.     }  
17. }  

原文链接http://blog.youkuaiyun.com/crazy__chen/article/details/46419385