leetcode_gym/_problems/matrixSearch.md

layout, title

layout	title
page	Matrix Search

Trick:

• think of matrix as 1D array
• turn 1D array index to row/col mapping
• ie: to access 16 (in array index 6), we know row=1 and col=2
• the magic leap is to realize row=6//4 and col=6%4 or (index//col_len and index%col_len)

Gotcha:

• if you don't get a handle on your off by one errors, you'll run into infinite loops
• row is mid//col_len, not mid//row_len

{% highlight python %}

mat = [

[1,2,3,4],

[5,6,7,8],

[9,10,11,12]

]

mat = 1,3,5,7],[10,11,16,20],[23,30,34,50

def searchMatrix(mat, target):

if not mat: return False

row_len=len(mat)
col_len=len(mat[0])

low = 0
high = row_len * col_len -1

while low<=high:
    
    mid = (low+high)//2
    
    print(low, high, mid)
    
    if mat[mid//col_len][mid%col_len]==target:
        return True
    elif mat[mid//col_len][mid%col_len]<target:
        low = mid+1
    else:
        high = mid-1

return False

print(searchMatrix(mat, 13))

{% endhighlight %}