Merge pull request #787 from 0xff-dev/1642

Add solution and test-cases for problem 1642

leetcode/1601-1700/1642.Furthest-Building-You-Can-Reach/README.md

@@ -1,28 +1,44 @@
 # [1642.Furthest Building You Can Reach][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+You are given an integer array `heights` representing the heights of buildings, some `bricks`, and some `ladders`.
+
+You start your journey from building `0` and move to the next building by possibly using bricks or ladders.
+
+While moving from building `i` to building `i+1` (**0-indexed**),
+
+- If the current building's height is **greater than or equal** to the next building's height, you do **not** need a ladder or bricks.
+- If the current building's height is **less than** the next building's height, you can either use **one ladder** or `(h[i+1] - h[i])` **bricks**.
+Return the furthest building index (0-indexed) you can reach if you use the given ladders and bricks optimally.
+
+**Example 1:**  
 
-**Example 1:**
+![1](./q4.gif)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: heights = [4,2,7,6,9,14,12], bricks = 5, ladders = 1
+Output: 4
+Explanation: Starting at building 0, you can follow these steps:
+- Go to building 1 without using ladders nor bricks since 4 >= 2.
+- Go to building 2 using 5 bricks. You must use either bricks or ladders because 2 < 7.
+- Go to building 3 without using ladders nor bricks since 7 >= 6.
+- Go to building 4 using your only ladder. You must use either bricks or ladders because 6 < 9.
+It is impossible to go beyond building 4 because you do not have any more bricks or ladders.
 ```
 
-## 题意
-> ...
+**Example 2:**
 
-## 题解
-
-### 思路1
-> ...
-Furthest Building You Can Reach
-```go
 ```
+Input: heights = [4,12,2,7,3,18,20,3,19], bricks = 10, ladders = 2
+Output: 7
+```
+
+**Example 3:**
 
+```
+Input: heights = [14,3,19,3], bricks = 17, ladders = 0
+Output: 3
+```
 
 ## 结语
 

leetcode/1601-1700/1642.Furthest-Building-You-Can-Reach/Solution.go

@@ -1,5 +1,76 @@
 package Solution
 
-func Solution(x bool) bool {
+import "container/heap"
+
+func Solution(heights []int, bricks int, ladders int) int {
+	// 1  2  3  4  5  6
+	// 4  0  1  1  1  9996  diff bsearchr+judge????
+	// b=4, l=1
+	diff := make([]int, len(heights))
+	for i := 1; i < len(heights); i++ {
+		if r := heights[i] - heights[i-1]; r > 0 {
+			diff[i] = r
+		}
+	}
+	l, r := 0, len(heights)
+	for l < r {
+		mid := (l + r) / 2
+		tmp := make([]int, mid+1)
+		for i := 0; i <= mid; i++ {
+			tmp[i] = diff[i]
+		}
+		if isOk1642(tmp, bricks, ladders) {
+			l = mid + 1
+		} else {
+			r = mid
+		}
+	}
+	if l != 0 {
+		l--
+	}
+	return l
+}
+
+type heap1642 []int
+
+func (h *heap1642) Len() int {
+	return len(*h)
+}
+
+func (h *heap1642) Less(i, j int) bool {
+	return (*h)[i] < (*h)[j]
+}
+func (h *heap1642) Swap(i, j int) {
+	(*h)[i], (*h)[j] = (*h)[j], (*h)[i]
+}
+func (h *heap1642) Push(x interface{}) {
+	*h = append(*h, x.(int))
+}
+
+func (h *heap1642) Pop() interface{} {
+	old := *h
+	l := len(old)
+	x := old[l-1]
+	*h = old[:l-1]
 	return x
 }
+func isOk1642(diffs []int, b, l int) bool {
+	h := heap1642(diffs)
+	heap.Init(&h)
+	for h.Len() > 0 {
+		top := heap.Pop(&h).(int)
+		if top <= 0 {
+			continue
+		}
+		if top <= b {
+			b -= top
+			continue
+		}
+		if l > 0 {
+			l--
+			continue
+		}
+		return false
+	}
+	return true
+}

leetcode/1601-1700/1642.Furthest-Building-You-Can-Reach/Solution_test.go

@@ -9,31 +9,33 @@ import (
 func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
-		name   string
-		inputs bool
-		expect bool
+		name            string
+		heights         []int
+		bricks, ladders int
+		expect          int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", []int{4, 2, 7, 6, 9, 14, 12}, 5, 1, 4},
+		{"TestCase2", []int{4, 12, 2, 7, 3, 18, 20, 3, 19}, 10, 2, 7},
+		{"TestCase3", []int{14, 3, 19, 3}, 17, 0, 3},
+		{"TestCase4", []int{7, 5, 13}, 0, 0, 1},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.heights, c.bricks, c.ladders)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v %v",
+					c.expect, got, c.heights, c.bricks, c.ladders)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }