40. 组合总和 II Combination Sum II

题目 <https://leetcode-cn.com/problems/combination-sum-ii/>

日常回溯法

只要题目是返回所有结果的，一般是回溯法；如果是返回有多少解的，就是动态规划了

因为要判断不能重复，所以需要先排序，之后回溯的时候跳过重复值

/**
 * Return an array of arrays of size *returnSize.
 * The sizes of the arrays are returned as *returnColumnSizes array.
 * Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().
 */
int **returnNums;
int *returnColSizes;
int returnLen;

void sort(int *nums,int numsSize){
    int left,right,mid,k;
    mid = 0;left=1,right=numsSize-1;
    if(left>right){
        return;
    }
    while(left<=right){
        while(left<=right&&nums[mid]<nums[right]) right--;
        if(left>right)  break;
        k = nums[mid];
        nums[mid] = nums[right];
        nums[right] = k;
        mid = right;
        right--;

        while(left<=right&&nums[mid]>nums[left]) left++;
        if(left>right)  break;
        k = nums[mid];
        nums[mid] = nums[left];
        nums[left] = k;
        mid = left;
        left++;
    }

    sort(nums,mid);
    sort(nums+mid+1,numsSize-mid-1);
}

void search(int* candidates, int candidatesSize,int target,int sum,int *tmp,int tmp_len,int index){
    if(sum > target){
        return;
    }

    if(sum == target){
        returnColSizes[returnLen] = tmp_len;
        returnNums[returnLen] = malloc(sizeof(int)*tmp_len);
        memcpy(returnNums[returnLen],tmp,sizeof(int)*tmp_len);
        returnLen++;
        return;
    }

    int i,j;
    for(i=index;i<candidatesSize;){
        tmp[tmp_len] = candidates[i];
        search(candidates,candidatesSize,target,sum + candidates[i],tmp,tmp_len+1,i+1);
        j = candidates[i];
        while(i<candidatesSize&&candidates[i]==j) i++;//跳过重复值
    }
}


int** combinationSum2(int* candidates, int candidatesSize, int target, int* returnSize, int** returnColumnSizes){
    sort(candidates,candidatesSize);

    returnNums = malloc(sizeof(int**) * 10000);
    returnColSizes = malloc(sizeof(int*) * 10000);
    returnLen = 0;
    int *tmp = malloc(sizeof(int) * candidatesSize);

    search(candidates,candidatesSize,target,0,tmp,0,0);

    free(tmp);
    *returnSize = returnLen;
    *returnColumnSizes = returnColSizes;
    return returnNums;
}