Memoization
Array
Dynamic Programming
Description
You are given several boxes
with different colors represented by different positive numbers.
You may experience several rounds to remove boxes until there is no box left. Each time you can choose some continuous boxes with the same color (i.e., composed of k
boxes, k >= 1
), remove them and get k * k
points.
Return the maximum points you can get .
Example 1:
Input: boxes = [1,3,2,2,2,3,4,3,1]
Output: 23
Explanation:
[1, 3, 2, 2, 2, 3, 4, 3, 1]
----> [1, 3, 3, 4, 3, 1] (3*3=9 points)
----> [1, 3, 3, 3, 1] (1*1=1 points)
----> [1, 1] (3*3=9 points)
----> [] (2*2=4 points)
Example 2:
Input: boxes = [1,1,1]
Output: 9
Example 3:
Input: boxes = [1]
Output: 1
Constraints:
1 <= boxes.length <= 100
1 <= boxes[i] <= 100
Solutions
Solution 1
Python3 Java C++ Go
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18 class Solution :
def removeBoxes ( self , boxes : List [ int ]) -> int :
@cache
def dfs ( i , j , k ):
if i > j :
return 0
while i < j and boxes [ j ] == boxes [ j - 1 ]:
j , k = j - 1 , k + 1
ans = dfs ( i , j - 1 , 0 ) + ( k + 1 ) * ( k + 1 )
for h in range ( i , j ):
if boxes [ h ] == boxes [ j ]:
ans = max ( ans , dfs ( h + 1 , j - 1 , 0 ) + dfs ( i , h , k + 1 ))
return ans
n = len ( boxes )
ans = dfs ( 0 , n - 1 , 0 )
dfs . cache_clear ()
return ans
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32 class Solution {
private int [][][] f ;
private int [] b ;
public int removeBoxes ( int [] boxes ) {
b = boxes ;
int n = b . length ;
f = new int [ n ][ n ][ n ] ;
return dfs ( 0 , n - 1 , 0 );
}
private int dfs ( int i , int j , int k ) {
if ( i > j ) {
return 0 ;
}
while ( i < j && b [ j ] == b [ j - 1 ] ) {
-- j ;
++ k ;
}
if ( f [ i ][ j ][ k ] > 0 ) {
return f [ i ][ j ][ k ] ;
}
int ans = dfs ( i , j - 1 , 0 ) + ( k + 1 ) * ( k + 1 );
for ( int h = i ; h < j ; ++ h ) {
if ( b [ h ] == b [ j ] ) {
ans = Math . max ( ans , dfs ( h + 1 , j - 1 , 0 ) + dfs ( i , h , k + 1 ));
}
}
f [ i ][ j ][ k ] = ans ;
return ans ;
}
}
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25 class Solution {
public :
int removeBoxes ( vector < int >& boxes ) {
int n = boxes . size ();
vector < vector < vector < int >>> f ( n , vector < vector < int >> ( n , vector < int > ( n )));
function < int ( int , int , int ) > dfs ;
dfs = [ & ]( int i , int j , int k ) {
if ( i > j ) return 0 ;
while ( i < j && boxes [ j ] == boxes [ j - 1 ]) {
-- j ;
++ k ;
}
if ( f [ i ][ j ][ k ]) return f [ i ][ j ][ k ];
int ans = dfs ( i , j - 1 , 0 ) + ( k