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explain the reason for reverse traversal

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Hayden-Chang
2022-05-08 14:20:09 +08:00
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problems/背包理论基础01背包-2.md
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@ -136,6 +136,7 @@ dp[1] = dp[1 - weight[0]] + value[0] = 15
不可以！
因为一维dp的写法，背包容量一定是要倒序遍历（原因上面已经讲了），如果遍历背包容量放在上一层，那么每个dp[j]就只会放入一个物品，即：背包里只放入了一个物品。
倒叙遍历的原因是，本质上还是一个对二维数组的遍历，并且右下角的值依赖上一层左上角的值，因此需要保证左边的值仍然是上一层的，从右向左覆盖。
（这里如果读不懂，就在回想一下dp[j]的定义，或者就把两个for循环顺序颠倒一下试试！）