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90 lines
2.2 KiB
Markdown
Executable File
90 lines
2.2 KiB
Markdown
Executable File
# [40. Combination Sum II](https://leetcode.com/problems/combination-sum-ii/)
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## 题目
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Given a collection of candidate numbers (`candidates`) and a target number (`target`), find all unique combinations in `candidates` where the candidate numbers sums to `target`.
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Each number in `candidates` may only be used **once** in the combination.
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**Note**:
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- All numbers (including `target`) will be positive integers.
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- The solution set must not contain duplicate combinations.
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**Example 1**:
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Input: candidates = [10,1,2,7,6,1,5], target = 8,
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A solution set is:
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[
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[1, 7],
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[1, 2, 5],
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[2, 6],
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[1, 1, 6]
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]
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**Example 2**:
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Input: candidates = [2,5,2,1,2], target = 5,
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A solution set is:
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[
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[1,2,2],
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[5]
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]
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## 题目大意
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给定一个数组 candidates 和一个目标数 target ，找出 candidates 中所有可以使数字和为 target 的组合。
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candidates 中的每个数字在每个组合中只能使用一次。
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## 解题思路
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- 题目要求出总和为 sum 的所有组合，组合需要去重。这一题是第 39 题的加强版，第 39 题中元素可以重复利用(重复元素可无限次使用)，这一题中元素只能有限次数的利用，因为存在重复元素，并且每个元素只能用一次(重复元素只能使用有限次)
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- 这一题和第 47 题类似，只不过元素可以反复使用。
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## 代码
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```go
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package leetcode
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import (
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"sort"
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)
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func combinationSum2(candidates []int, target int) [][]int {
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if len(candidates) == 0 {
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return [][]int{}
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}
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c, res := []int{}, [][]int{}
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sort.Ints(candidates) // 这里是去重的关键逻辑
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findcombinationSum2(candidates, target, 0, c, &res)
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return res
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}
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func findcombinationSum2(nums []int, target, index int, c []int, res *[][]int) {
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if target == 0 {
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b := make([]int, len(c))
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copy(b, c)
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*res = append(*res, b)
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return
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}
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for i := index; i < len(nums); i++ {
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if i > index && nums[i] == nums[i-1] { // 这里是去重的关键逻辑,本次不取重复数字，下次循环可能会取重复数字
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continue
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}
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if target >= nums[i] {
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c = append(c, nums[i])
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findcombinationSum2(nums, target-nums[i], i+1, c, res)
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c = c[:len(c)-1]
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}
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}
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}
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```
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