LeetCode-39-组合总和-C语言

/*
 * 算法思想：
 * 回溯算法，套用回溯框架，很容易得出答案，详见代码注释。
 *
 *
 */

void rec(int *arr, int len, int index, int *stack, int *stack_index, 
         int target, int **ret, int *ret_index, int *ret_size){
    if(index >= len || target < 0 ) return;
    
    /* 符合条件，添加到答案中 */
    if(target == 0){
        ret[(*ret_index)] = (int *)malloc(sizeof(int) * (*stack_index));
        ret_size[(*ret_index)] = *stack_index;
        memcpy(ret[(*ret_index)], stack, (*stack_index)*sizeof(int));
        (*ret_index)++;
        return;
    }    

    /* 回溯循环，注意从index开始，因为可以重复使用相同的元素 */
    for(; index<len; index++){
        target -= arr[index];
        stack[(*stack_index)++] = arr[index];

        rec(arr, len, index, stack, stack_index, target, ret, ret_index, ret_size);

        (*stack_index)--;
        target += arr[index];        
    }
}

#define LEN 0xffff

int** combinationSum(int* arr, int len, int target, int* returnSize, int** returnColumnSizes){
    int *stack = (int *)malloc(sizeof(int) * LEN);
    int stack_index = 0;
    int **ret = (int **)malloc(sizeof(int *) * LEN);
    int ret_index = 0;
    int *ret_size = (int *)malloc(sizeof(int) * LEN);
    *returnColumnSizes = ret_size;
    
    rec(arr, len, 0, stack, &stack_index, target, ret, &ret_index, ret_size);
    
    //printf("ret_index = %d \n", ret_index);
    
    *returnSize = ret_index;
      free(stack);
    return ret;
}