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;
}