1049. Last Stone Weight II

We have a collection of rocks, each rock has a positive integer weight.

Each turn, we choose any two rocks and smash them together.  Suppose the stones have weights `x` and `y` with `x <= y`.  The result of this smash is:

• If `x == y`, both stones are totally destroyed;
• If `x != y`, the stone of weight `x` is totally destroyed, and the stone of weight `y` has new weight `y-x`.

At the end, there is at most 1 stone left.  Return the smallest possible weight of this stone (the weight is 0 if there are no stones left.)

Example 1:

```Input: [2,7,4,1,8,1]
Output: 1
Explanation:
We can combine 2 and 4 to get 2 so the array converts to [2,7,1,8,1] then,
we can combine 7 and 8 to get 1 so the array converts to [2,1,1,1] then,
we can combine 2 and 1 to get 1 so the array converts to [1,1,1] then,
we can combine 1 and 1 to get 0 so the array converts to [1] then that's the optimal value.
```

Note:

1. `1 <= stones.length <= 30`
2. `1 <= stones[i] <= 100`

1049. Last Stone Weight II
``````struct Solution;

impl Solution {
fn last_stone_weight_ii(stones: Vec<i32>) -> i32 {
let sum = stones.iter().sum::<i32>() as usize;
let mut dp = vec![false; sum + 1];
dp[0] = true;
let n = stones.len();
for i in 0..n {
for j in (1..=sum).rev() {
if j >= stones[i] as usize && dp[j - stones[i] as usize] {
dp[j] = true;
}
}
}
let mut res = sum;
for i in 0..=sum / 2 {
if dp[i] {
res = res.min(sum - 2 * i);
}
}
res as i32
}
}

#[test]
fn test() {
let stones = vec![2, 7, 4, 1, 8, 1];
let res = 1;
assert_eq!(Solution::last_stone_weight_ii(stones), res);
}
``````