LeetCode 1011。二进制搜索，C++和Python相同的思想，但不同的输出

Question

有人能看看我的CPP代码吗？它来自于这个问题：https://leetcode.com/problems/capacity-to-ship-packages-within-d-days/我感到非常沮丧，因为虽然我的python代码可以工作，但是我的cpp代码不能像往常一样工作。忧郁:相同的想法，不同的结果。简直快让我疯了。

正确的输出应该是15。我的Python代码返回正确的输出15，而我的CPP代码返回错误的输出10。

我的python代码：

def cnt_days(weights, k):
        total, cnt = 0, 1
        for w in weights:
            if total + w > k:
                total = 0
                cnt += 1
            total += w
        print(total, cnt)
        return cnt

def shipWithinDays(weights, D):
    left = max(weights)
    right = max(weights) * len(weights) // D + 1

    while left < right:
        mid = left + (right - left) // 2
        if cnt_days(weights, mid) > D:
            left = mid + 1
        else:
            right = mid
    return left           


if __name__ == "__main__":
    print(shipWithinDays([1,2,3,4,5,6,7,8,9,10], 5))

我的cpp代码：

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int cnt_days(vector<int>& weights, int K)
{
    int total = 0, cnt = 1;
    for (int w: weights)
    {
        if (total + w > K) 
        {
            total = 0;
            cnt++;
        }
        else total += w;
    }
    cout << total <<" "<<  cnt << endl;
    return cnt;
}

int shipWithinDays(vector<int>& weights, int D)
{
    int maximum = *max_element(weights.begin(), weights.end());
    int left = maximum;
    int right = maximum * weights.size() / D + 1;
    while (left < right)
    {
        int mid = left + (right - left)/2;
        if (cnt_days(weights, mid) > D)
            left = mid + 1;
        else
            right = mid;
    }
    return left;    
}

int main()
{
    vector<int> weights = {1,2,3,4,5,6,7,8,9,10};
    int D = 5;
    cout << shipWithinDays(weights, D) << endl;
    return 0;
}

Answer 1

移除其他的

else total += w;

应该是

total += w;

Answer 2

也许，您可以对您的c++解决方案进行更简单的二进制搜索：

#include <vector>

class Solution {
public:
    int shipWithinDays(std::vector<int>& weights, int d) {
        int lo = 0;
        int hi = INT_MAX;

        for (int weight : weights) {
            lo = max(lo, weight);
        }

        while (lo < hi) {
            int mid = lo + (hi - lo) / 2;
            int required = 1;
            int cur = 0;

            for (int index = 0; index < weights.size() && required <= d; cur += weights[index++])
                if (cur + weights[index] > mid) {
                    cur = 0;
                    required++;
                }


            if (required > d) {
                lo = mid + 1;

            } else {
                hi = mid;
            }

        }

        return lo;
    }
};

或者使用基本的按位操作：

class Solution {
public:
    int shipWithinDays(vector<int> &weights, int d) {
        int lo = 0;
        int hi = INT_MAX;

        for (int weight : weights)
            lo = max(lo, weight);

        while (lo < hi) {
            int mid = lo + ((hi - lo) >> 1);
            int required = 1;
            int cur = 0;

            for (int index = 0; index < weights.size() && required <= d; cur += weights[index++])
                if (cur + weights[index] > mid)
                    cur = 0, required++;

            if (required > d)
                lo = -~mid;

            else
                hi = mid;

        }

        return lo;
    }
};

同样，python也是这样：

from typing import List

class Solution:
    def shipWithinDays(self, weights: List[int], d: int) -> int:
        lo, hi = max(weights), sum(weights)
        while lo < hi:
            mid = lo + ((hi - lo) >> 1) # or mid = (lo + hi) // 2 || mid = lo + (hi - lo) // 2
            cur, required = 0, 1
            for weight in weights:
                if cur + weight > mid:
                    required += 1
                    cur = 0
                cur += weight
            if required > d:
                lo = -~mid # simply lo = mid + 1
            else:
                hi = mid

        return lo

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