The sword refers to the offer programming question-1

1. Lookup in a 2D array

Topic description

In a two-dimensional array, each row is sorted in increasing order from left to right, and each column is sorted in increasing order from top to bottom. Please complete a function, input such a two-dimensional array and an integer, and determine whether the array contains the integer.

Ideas:

利用二维数组由上到下，由左到右递增的规律，

那么选取右上角a[row][col]与target进行比较，如果等于就直接找到，

当target小于元素a[row][col]时，那么target必定在元素a所在行的左边,

即col--；

当target大于元素a[row][col]时，那么target必定在元素a所在列的下边,

即row++；

    public class Solution {

　　public boolean Find(int target, int [][] array) {
        int row=0;
        int col=array[0].length-1;
        while(row<=array.length-1&&col>=0){
            if(target==array[row][col])
                return true;
            else if(target>array[row][col])
                row++;
            else
                col--;
        }
        return false;
 
    }

 }

 

Notice:

For a 2D array:

int[][] arr = {  
        {2,3,4},  
        {4,5,6},  
        {7,8,9}  
    };  

int rows = i.length;//行数
int columns = i[0].length;//列数

[[]] Such an array represents 1 for the number of rows and 0 for the number of columns.