leetcode 46 全排列 回溯法 C语言实现

题目

leetcode 46
给定一个没有重复数字的序列,返回其所有可能的全排列。

示例:
输入: [1,2,3]
输出:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]
思路:回溯法

int flag[1024] = {0};
void dfs(int *nums, int numsSize, int i, int arr[], int m, int **res, int *ind) {
    if (m == numsSize) {
        for (int i = 0; i < numsSize; i++) {
            res[*ind][i] = arr[i];
        }
        (*ind)++;
        return ;
    }
    for (int i = 0; i < numsSize; i++) {
        if (flag[i] == 1) continue;
        arr[m] = nums[i];
        flag[i] = 1;
        dfs(nums, numsSize, i, arr, m + 1, res, ind);
        flag[i] = 0;
    }
}
int** permute(int* nums, int numsSize, int* returnSize, int** returnColumnSizes){
    *returnSize = 0;
    if (numsSize == 0) return 0;
    int count = 1, k = 1;
    while (k <= numsSize) {
        count = count * k;;
        k++;
    }
    int **res = (int **)malloc(sizeof(int *) * count);
    *returnColumnSizes = (int *)malloc(sizeof(int) * count);
    for (int i = 0; i < count; i++) {
        res[i] = (int *)malloc(sizeof(int) * (numsSize + 5));
        (*returnColumnSizes)[i] = numsSize;
    }
    int arr[numsSize + 5], ind = 0;
    dfs(nums, numsSize, 0, arr, 0, res, &ind);
    *returnSize = ind;
    return res;
}

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