Competitive Programming Editorials

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Constructive turns competitive programming editorials into interactive, step-by-step visualizations so the solution actually clicks.

Browse Editorials
solve.cpp
1for i in range(1, n+1):
2 for j in range(1, W+1):
3 if w[i-1] <= j:
4 dp[i][j] = max(
5 dp[i-1][j],
6 dp[i-1][j-w[i-1]] + v[i-1]
7 )
8 else:
9 dp[i][j] = dp[i-1][j]
Memory Inspector
w=0w=1w=2w=3w=4w=5
i=0
0
0
0
0
0
0
i=1
0
1
1
1
1
1
i=2
0
1
1
2
2
2
i=3
0
1
1
2
2
3
i=4
0
1
2
2
3
3

Insight: At dp[3][5], we compare the previous best (2) vs taking item 3. Taking it yields 3, which wins.

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We walk you through the reasoning — the leap from brute force to the elegant solution — so you can reproduce it on new problems.

Problem First

Each editorial starts with the problem statement and key observations — building context before jumping into code.

LaTeX & Math

Full KaTeX support for recurrences, proofs, and complexity analysis — rendered beautifully inline.

dp[i][j]=max⁡(dp[i−1][j],dp[i−1][j−wi−1]+vi−1)dp[i][j] = \max( dp[i-1][j], dp[i-1][j-w_{i-1}] + v_{i-1} )

Library

Recent Editorials

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DP

A. Cut Ribbon

Codeforces 189A. Maximize the number of ribbon pieces. A quintessential introduction to 1D dynamic programming.

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C. Dijkstra?

Codeforces 20C. Find the shortest path from vertex 1 to vertex N and reconstruct the exact path using a priority queue.

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Data Structures

E. Xenia and Bit Operations

Codeforces 339D. Maintain alternating bitwise OR and XOR operations on an array under point updates.

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Dynamic Programming
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Segment Trees
Trie
Geometry

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