Use D&C when: DP has layers: dp[g][i]=minj<i(dp[g−1][j]+cost(j,i)). Partitioning into k groups. Use Knuth when: DP is interval-based: dp[i][j]=mini≤k≤j(dp[i][k−1]+dp[k+1][j])+cost. Combining subproblems. Both need: Cost satisfies the quadrangle inequality.
If unsure which, check the recurrence structure. Layers = D&C. Intervals = Knuth.