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Discrete items block
In 0/1 knapsack, items are indivisible. Greedy by ratio fails.
Example: items = [(60,10), (100,20), (120,30)], W = 50. Greedy: take item 1 (ratio P2), item 2 (ratio P4). Total weight: 30, value: 160. Item 3 does not fit.
But items 2 + 3: weight = 50, value = 220. Better! The discrete constraint causes blocking. Use DP for 0/1 knapsack.
