README_EN.md

17.08. Circus Tower

中文文档

Description

A circus is designing a tower routine consisting of people standing atop one anoth­er's shoulders. For practical and aesthetic reasons, each person must be both shorter and lighter than the person below him or her. Given the heights and weights of each person in the circus, write a method to compute the largest possible number of people in such a tower.

Example:

Input: height = [65,70,56,75,60,68] weight = [100,150,90,190,95,110]
Output: 6
Explanation: The longest tower is length 6 and includes from top to bottom: (56,90), (60,95), (65,100), (68,110), (70,150), (75,190)

Note:

• height.length == weight.length <= 10000

Solutions

Python3

class BinaryIndexedTree:
    def __init__(self, n):
        self.n = n
        self.c = [0] * (n + 1)

    def update(self, x, delta):
        while x <= self.n:
            self.c[x] = max(self.c[x], delta)
            x += x & -x

    def query(self, x):
        s = 0
        while x:
            s = max(s, self.c[x])
            x -= x & -x
        return s


class Solution:
    def bestSeqAtIndex(self, height: List[int], weight: List[int]) -> int:
        arr = list(zip(height, weight))
        arr.sort(key=lambda x: (x[0], -x[1]))
        alls = sorted({w for _, w in arr})
        m = {w: i for i, w in enumerate(alls, 1)}
        tree = BinaryIndexedTree(len(m))
        ans = 1
        for _, w in arr:
            x = m[w]
            t = tree.query(x - 1) + 1
            ans = max(ans, t)
            tree.update(x, t)
        return ans

Java

class BinaryIndexedTree {
    private int n;
    private int[] c;

    public BinaryIndexedTree(int n) {
        this.n = n;
        c = new int[n + 1];
    }

    public void update(int x, int val) {
        while (x <= n) {
            this.c[x] = Math.max(this.c[x], val);
            x += x & -x;
        }
    }

    public int query(int x) {
        int s = 0;
        while (x > 0) {
            s = Math.max(s, this.c[x]);
            x -= x & -x;
        }
        return s;
    }
}

class Solution {
    public int bestSeqAtIndex(int[] height, int[] weight) {
        int n = height.length;
        int[][] arr = new int[n][2];
        for (int i = 0; i < n; ++i) {
            arr[i] = new int[] {height[i], weight[i]};
        }
        Arrays.sort(arr, (a, b) -> a[0] == b[0] ? b[1] - a[1] : a[0] - b[0]);
        Set<Integer> s = new HashSet<>();
        for (int[] e : arr) {
            s.add(e[1]);
        }
        List<Integer> alls = new ArrayList<>(s);
        Collections.sort(alls);
        Map<Integer, Integer> m = new HashMap<>(alls.size());
        for (int i = 0; i < alls.size(); ++i) {
            m.put(alls.get(i), i + 1);
        }
        BinaryIndexedTree tree = new BinaryIndexedTree(alls.size());
        int ans = 1;
        for (int[] e : arr) {
            int x = m.get(e[1]);
            int t = tree.query(x - 1) + 1;
            ans = Math.max(ans, t);
            tree.update(x, t);
        }
        return ans;
    }
}

C++

class BinaryIndexedTree {
public:
    BinaryIndexedTree(int _n)
        : n(_n)
        , c(_n + 1) {}

    void update(int x, int val) {
        while (x <= n) {
            c[x] = max(c[x], val);
            x += x & -x;
        }
    }

    int query(int x) {
        int s = 0;
        while (x > 0) {
            s = max(s, c[x]);
            x -= x & -x;
        }
        return s;
    }

private:
    int n;
    vector<int> c;
};

class Solution {
public:
    int bestSeqAtIndex(vector<int>& height, vector<int>& weight) {
        int n = height.size();
        vector<pair<int, int>> people;
        for (int i = 0; i < n; ++i) {
            people.emplace_back(height[i], weight[i]);
        }
        sort(people.begin(), people.end(), [](const pair<int, int>& a, const pair<int, int>& b) {
            if (a.first == b.first) {
                return a.second > b.second;
            }
            return a.first < b.first;
        });
        vector<int> alls = weight;
        sort(alls.begin(), alls.end());
        alls.erase(unique(alls.begin(), alls.end()), alls.end());
        BinaryIndexedTree tree(alls.size());
        int ans = 1;
        for (auto& [_, w] : people) {
            int x = lower_bound(alls.begin(), alls.end(), w) - alls.begin() + 1;
            int t = tree.query(x - 1) + 1;
            ans = max(ans, t);
            tree.update(x, t);
        }
        return ans;
    }
};

Go

type BinaryIndexedTree struct {
	n int
	c []int
}

func newBinaryIndexedTree(n int) *BinaryIndexedTree {
	c := make([]int, n+1)
	return &BinaryIndexedTree{n, c}
}

func (this *BinaryIndexedTree) update(x, val int) {
	for x <= this.n {
		if this.c[x] < val {
			this.c[x] = val
		}
		x += x & -x
	}
}

func (this *BinaryIndexedTree) query(x int) int {
	s := 0
	for x > 0 {
		if s < this.c[x] {
			s = this.c[x]
		}
		x -= x & -x
	}
	return s
}

func bestSeqAtIndex(height []int, weight []int) int {
	n := len(height)
	people := make([][2]int, n)
	s := map[int]bool{}
	for i := range people {
		people[i] = [2]int{height[i], weight[i]}
		s[weight[i]] = true
	}
	sort.Slice(people, func(i, j int) bool {
		a, b := people[i], people[j]
		return a[0] < b[0] || a[0] == b[0] && a[1] > b[1]
	})
	alls := make([]int, 0, len(s))
	for k := range s {
		alls = append(alls, k)
	}
	sort.Ints(alls)
	tree := newBinaryIndexedTree(len(alls))
	ans := 1
	for _, p := range people {
		x := sort.SearchInts(alls, p[1]) + 1
		t := tree.query(x-1) + 1
		ans = max(ans, t)
		tree.update(x, t)
	}
	return ans
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

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