C语言 | Leetcode C语言题解之第321题拼接最大数

题目：

题解：

int compare(int* subseq1, int subseq1Size, int index1, int* subseq2, int subseq2Size, int index2) {
    while (index1 < subseq1Size && index2 < subseq2Size) {
        int difference = subseq1[index1] - subseq2[index2];
        if (difference != 0) {
            return difference;
        }
        index1++;
        index2++;
    }
    return (subseq1Size - index1) - (subseq2Size - index2);
}

int* merge(int* subseq1, int subseq1Size, int* subseq2, int subseq2Size) {
    if (subseq1Size == 0) {
        return subseq2;
    }
    if (subseq2Size == 0) {
        return subseq1;
    }
    int mergeLength = subseq1Size + subseq2Size;
    int* merged = malloc(sizeof(int) * (subseq1Size + subseq2Size));
    int index1 = 0, index2 = 0;
    for (int i = 0; i < mergeLength; i++) {
        if (compare(subseq1, subseq1Size, index1, subseq2, subseq2Size, index2) > 0) {
            merged[i] = subseq1[index1++];
        } else {
            merged[i] = subseq2[index2++];
        }
    }
    return merged;
}

int* MaxSubsequence(int* nums, int numsSize, int k) {
    int* stack = malloc(sizeof(int) * k);
    memset(stack, 0, sizeof(int) * k);
    int top = -1;
    int remain = numsSize - k;
    for (int i = 0; i < numsSize; i++) {
        int num = nums[i];
        while (top >= 0 && stack[top] < num && remain > 0) {
            top--;
            remain--;
        }
        if (top < k - 1) {
            stack[++top] = num;
        } else {
            remain--;
        }
    }
    return stack;
}

void swap(int** a, int** b) {
    int* tmp = *a;
    *a = *b, *b = tmp;
}

int* maxNumber(int* nums1, int nums1Size, int* nums2, int nums2Size, int k, int* returnSize) {
    int* maxSubsequence = malloc(sizeof(int) * k);
    memset(maxSubsequence, 0, sizeof(int) * k);
    *returnSize = k;
    int start = fmax(0, k - nums2Size), end = fmin(k, nums1Size);
    for (int i = start; i <= end; i++) {
        int* subseq1 = MaxSubsequence(nums1, nums1Size, i);
        int* subseq2 = MaxSubsequence(nums2, nums2Size, k - i);
        int* curMaxSubsequence = merge(subseq1, i, subseq2, k - i);
        if (compare(curMaxSubsequence, k, 0, maxSubsequence, k, 0) > 0) {
            swap(&curMaxSubsequence, &maxSubsequence);
        }
    }
    return maxSubsequence;
}