finish Problem 40

通过了测试。

Author: aQua

Algorithms/0039.combination-sum/combination-sum.go

@@ -19,10 +19,8 @@ func cs(candidates, solution []int, target int, result *[][]int) {
 		*result = append(*result, solution)
 	}
 
-	if target < 0 || len(candidates) == 0 || target < candidates[0] {
+	if len(candidates) == 0 || target < candidates[0] {
 		// target < candidates[0] 这个是因为candidates是排序好的
-		// 否则，就应该是 target < min(candidates...)
-		// 其实，不要这个判断条件，也能成功
 		return
 	}
 

Algorithms/0040.combination-sum-ii/100.png

@@ -6,8 +6,8 @@ Given a collection of candidate numbers (C) and a target number (T), find all un
 Each number in C may only be used once in the combination.
 
 Note:
-All numbers (including target) will be positive integers.
-The solution set must not contain duplicate combinations.
+1. All numbers (including target) will be positive integers.
+1. The solution set must not contain duplicate combinations.
 For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8, 
 A solution set is:
 ``` 
@@ -19,8 +19,8 @@ A solution set is:
 ]
 ```
 ## 解题思路
-
+这一题是[39. Combination Sum](https://leetcode.com/problems/combination-sum/)的变种。区别在于，元素不能重复使用。所以在划分的时候，对candidates的处理也不同。
 
 ## 总结
-
-
+又提交了一次，一不小心就迎来了人生的第一个100%，主要的功劳在leetcode服务器。
+![100%](100.png)

Algorithms/0040.combination-sum-ii/README.md

@@ -7,20 +7,18 @@ func combinationSum2(candidates []int, target int) [][]int {
 
 	res := [][]int{}
 	solution := []int{}
-	cs(candidates, solution, target, &res)
+	cs2(candidates, solution, target, &res)
 
 	return res
 }
 
-func cs(candidates, solution []int, target int, result *[][]int) {
+func cs2(candidates, solution []int, target int, result *[][]int) {
 	if target == 0 {
 		*result = append(*result, solution)
 	}
 
-	if target < 0 || len(candidates) == 0 || target < candidates[0] {
-		// target < candidates[0] 这个是因为candidates是排序好的
-		// 否则，就应该是 target < min(candidates...)
-		// 其实，不要这个判断条件，也能成功
+	if len(candidates) == 0 || target < candidates[0] {
+		// target < candidates[0] 因为candidates是排序好的
 		return
 	}
 
@@ -29,7 +27,17 @@ func cs(candidates, solution []int, target int, result *[][]int) {
 	// 可以注释掉以下语句，运行单元测试，查看错误发生。
 	solution = solution[:len(solution):len(solution)]
 
-	cs(candidates, append(solution, candidates[0]), target-candidates[0], result)
+	// 去掉已使用了的candidates[0]
+	cs2(candidates[1:], append(solution, candidates[0]), target-candidates[0], result)
 
-	cs(candidates[1:], solution, target, result)
+	// 不使用candidates[0]的话，就要把所有和candidates[0]相等的元素都去掉。
+	cs2(next(candidates), solution, target, result)
+}
+
+func next(candidates []int) []int {
+	i := 0
+	for i+1 < len(candidates) && candidates[i] == candidates[i+1] {
+		i++
+	}
+	return candidates[i+1:]
 }

Algorithms/0040.combination-sum-ii/combination-sum-ii.go

@@ -33,13 +33,19 @@ func Test_Problem0039(t *testing.T) {
 		question{
 			para{[]int{10, 1, 2, 7, 6, 1, 5}, 8},
 			ans{[][]int{
-				[]int{1, 7},
+				[]int{1, 1, 6},
 				[]int{1, 2, 5},
+				[]int{1, 7},
 				[]int{2, 6},
-				[]int{1, 1, 6},
 			}},
 		},
 
+		question{
+			para{[]int{1}, 1},
+			ans{[][]int{
+				[]int{1},
+			}},
+		},
 		// 如需多个测试，可以复制上方元素。
 	}