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315. Count of Smaller Numbers After Self

Description

Given an integer array nums, return an integer array counts where counts[i] is the number of smaller elements to the right of nums[i].

 

Example 1:

Input: nums = [5,2,6,1]
Output: [2,1,1,0]
Explanation:
To the right of 5 there are 2 smaller elements (2 and 1).
To the right of 2 there is only 1 smaller element (1).
To the right of 6 there is 1 smaller element (1).
To the right of 1 there is 0 smaller element.

Example 2:

Input: nums = [-1]
Output: [0]

Example 3:

Input: nums = [-1,-1]
Output: [0,0]

 

Constraints:

  • 1 <= nums.length <= 105
  • -104 <= nums[i] <= 104

Solutions

Solution 1

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

    @staticmethod
    def lowbit(x):
        return x & -x

    def update(self, x, delta):
        while x <= self.n:
            self.c[x] += delta
            x += BinaryIndexedTree.lowbit(x)

    def query(self, x):
        s = 0
        while x > 0:
            s += self.c[x]
            x -= BinaryIndexedTree.lowbit(x)
        return s


class Solution:
    def countSmaller(self, nums: List[int]) -> List[int]:
        alls = sorted(set(nums))
        m = {v: i for i, v in enumerate(alls, 1)}
        tree = BinaryIndexedTree(len(m))
        ans = []
        for v in nums[::-1]:
            x = m[v]
            tree.update(x, 1)
            ans.append(tree.query(x - 1))
        return ans[::-1]
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class Solution {
    public List<Integer> countSmaller(int[] nums) {
        Set<Integer> s = new HashSet<>();
        for (int v : nums) {
            s.add(v);
        }
        List<Integer> alls = new ArrayList<>(s);
        alls.sort(Comparator.comparingInt(a -> a));
        int n = alls.size();
        Map<Integer, Integer> m = new HashMap<>(n);
        for (int i = 0; i < n; ++i) {
            m.put(alls.get(i), i + 1);
        }
        BinaryIndexedTree tree = new BinaryIndexedTree(n);
        LinkedList<Integer> ans = new LinkedList<>();
        for (int i = nums.length - 1; i >= 0; --i) {
            int x = m.get(nums[i]);
            tree.update(x, 1);
            ans.addFirst(tree.query(x - 1));
        }
        return ans;
    }
}

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 delta) {
        while (x <= n) {
            c[x] += delta;
            x += lowbit(x);
        }
    }

    public int query(int x) {
        int s = 0;
        while (x > 0) {
            s += c[x];
            x -= lowbit(x);
        }
        return s;
    }

    public static int lowbit(int x) {
        return x & -x;
    }
}
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class BinaryIndexedTree {
public:
    int n;
    vector<int> c;

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

    void update(int x, int delta) {
        while (x <= n) {
            c[x] += delta;
            x += lowbit(x);
        }
    }

    int query(int x) {
        int s = 0;
        while (x > 0) {
            s += c[x];
            x -= lowbit(x);
        }
        return s;
    }

    int lowbit(int x) {
        return x & -x;
    }
};

class Solution {
public:
    vector<int> countSmaller(vector<int>& nums) {
        unordered_set<int> s(nums.begin(), nums.end());
        vector<int> alls(s.begin(), s.end());
        sort(alls.begin(), alls.end());
        unordered_map<int, int> m;
        int n = alls.size();
        for (int i = 0; i < n; ++i) m[alls[i]] = i + 1;
        BinaryIndexedTree* tree = new BinaryIndexedTree(n);
        vector<int> ans(nums.size());
        for (int i = nums.size() - 1; i >= 0; --i) {
            int x = m[nums[i]];
            tree->update(x, 1);
            ans[i] = tree->query(x - 1);
        }
        return ans;
    }
};
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type BinaryIndexedTree struct {
    n int
    c []int
}

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

func (this *BinaryIndexedTree) lowbit(x int) int {
    return x & -x
}

func (this *BinaryIndexedTree) update(x, delta int) {
    for x <= this.n {
        this.c[x] += delta
        x += this.lowbit(x)
    }
}

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

func countSmaller(nums []int) []int {
    s := make(map[int]bool)
    for _, v := range nums {
        s[v] = true
    }
    var alls []int
    for v := range s {
        alls = append(alls, v)
    }
    sort.Ints(alls)
    m := make(map[int]int)
    for i, v := range alls {
        m[v] = i + 1
    }
    ans := make([]int, len(nums))
    tree := newBinaryIndexedTree(len(alls))
    for i := len(nums) - 1; i >= 0; i-- {
        x := m[nums[i]]
        tree.update(x, 1)
        ans[i] = tree.query(x - 1)
    }
    return ans
}

Solution 2

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class Node:
    def __init__(self):
        self.l = 0
        self.r = 0
        self.v = 0


class SegmentTree:
    def __init__(self, n):
        self.tr = [Node() for _ in range(n << 2)]
        self.build(1, 1, n)

    def build(self, u, l, r):
        self.tr[u].l = l
        self.tr[u].r = r
        if l == r:
            return
        mid = (l + r) >> 1
        self.build(u << 1, l, mid)
        self.build(u << 1 | 1, mid + 1, r)

    def modify(self, u, x, v):
        if self.tr[u].l == x and self.tr[u].r == x:
            self.tr[u].v += v
            return
        mid = (self.tr[u].l + self.tr[u].r) >> 1
        if x <= mid:
            self.modify(u << 1, x, v)
        else:
            self.modify(u << 1 | 1, x, v)
        self.pushup(u)

    def query(self, u, l, r):
        if self.tr[u].l >= l and self.tr[u].r <= r:
            return self.tr[u].v
        mid = (self.tr[u].l + self.tr[u].r) >> 1
        v = 0
        if l <= mid:
            v += self.query(u << 1, l, r)
        if r > mid:
            v += self.query(u << 1 | 1, l, r)
        return v

    def pushup(self, u):
        self.tr[u].v = self.tr[u << 1].v + self.tr[u << 1 | 1].v


class Solution:
    def countSmaller(self, nums: List[int]) -> List[int]:
        s = sorted(set(nums))
        m = {v: i for i, v in enumerate(s, 1)}
        tree = SegmentTree(len(s))
        ans = []
        for v in nums[::-1]:
            x = m[v]
            ans.append(tree.query(1, 1, x - 1))
            tree.modify(1, x, 1)
        return ans[::-1]
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class Solution {
    public List<Integer> countSmaller(int[] nums) {
        Set<Integer> s = new HashSet<>();
        for (int v : nums) {
            s.add(v);
        }
        List<Integer> alls = new ArrayList<>(s);
        alls.sort(Comparator.comparingInt(a -> a));
        int n = alls.size();
        Map<Integer, Integer> m = new HashMap<>(n);
        for (int i = 0; i < n; ++i) {
            m.put(alls.get(i), i + 1);
        }
        SegmentTree tree = new SegmentTree(n);
        LinkedList<Integer> ans = new LinkedList<>();
        for (int i = nums.length - 1; i >= 0; --i) {
            int x = m.get(nums[i]);
            tree.modify(1, x, 1);
            ans.addFirst(tree.query(1, 1, x - 1));
        }
        return ans;
    }
}

class Node {
    int l;
    int r;
    int v;
}

class SegmentTree {
    private Node[] tr;

    public SegmentTree(int n) {
        tr = new Node[4 * n];
        for (int i = 0; i < tr.length; ++i) {
            tr[i] = new Node();
        }
        build(1, 1, n);
    }

    public void build(int u, int l, int r) {
        tr[u].l = l;
        tr[u].r = r;
        if (l == r) {
            return;
        }
        int mid = (l + r) >> 1;
        build(u << 1, l, mid);
        build(u << 1 | 1, mid + 1, r);
    }

    public void modify(int u, int x, int v) {
        if (tr[u].l == x && tr[u].r == x) {
            tr[u].v += v;
            return;
        }
        int mid = (tr[u].l + tr[u].r) >> 1;
        if (x <= mid) {
            modify(u << 1, x, v);
        } else {
            modify(u << 1 | 1, x, v);
        }
        pushup(u);
    }

    public void pushup(int u) {
        tr[u].v = tr[u << 1].v + tr[u << 1 | 1].v;
    }

    public int query(int u, int l, int r) {
        if (tr[u].l >= l && tr[u].r <= r) {
            return tr[u].v;
        }
        int mid = (tr[u].l + tr[u].r) >> 1;
        int v = 0;
        if (l <= mid) {
            v += query(u << 1, l, r);
        }
        if (r > mid) {
            v += query(u << 1 | 1, l, r);
        }
        return v;
    }
}
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class Node {
public:
    int l;
    int r;
    int v;
};

class SegmentTree {
public:
    vector<Node*> tr;

    SegmentTree(int n) {
        tr.resize(4 * n);
        for (int i = 0; i < tr.size(); ++i) tr[i] = new Node();
        build(1, 1, n);
    }

    void build(int u, int l, int r) {
        tr[u]->l = l;
        tr[u]->r = r;
        if (l == r) return;
        int mid = (l + r) >> 1;
        build(u << 1, l, mid);
        build(u << 1 | 1, mid + 1, r);
    }

    void modify(int u, int x, int v) {
        if (tr[u]->l == x && tr[u]->r == x) {
            tr[u]->v += v;
            return;
        }
        int mid = (tr[u]->l + tr[u]->r) >> 1;
        if (x <= mid)
            modify(u << 1, x, v);
        else
            modify(u << 1 | 1, x, v);
        pushup(u);
    }

    void pushup(int u) {
        tr[u]->v = tr[u << 1]->v + tr[u << 1 | 1]->v;
    }

    int query(int u, int l, int r) {
        if (tr[u]->l >= l && tr[u]->r <= r) return tr[u]->v;
        int mid = (tr[u]->l + tr[u]->r) >> 1;
        int v = 0;
        if (l <= mid) v += query(u << 1, l, r);
        if (r > mid) v += query(u << 1 | 1, l, r);
        return v;
    }
};

class Solution {
public:
    vector<int> countSmaller(vector<int>& nums) {
        unordered_set<int> s(nums.begin(), nums.end());
        vector<int> alls(s.begin(), s.end());
        sort(alls.begin(), alls.end());
        unordered_map<int, int> m;
        int n = alls.size();
        for (int i = 0; i < n; ++i) m[alls[i]] = i + 1;
        SegmentTree* tree = new SegmentTree(n);
        vector<int> ans(nums.size());
        for (int i = nums.size() - 1; i >= 0; --i) {
            int x = m[nums[i]];
            tree->modify(1, x, 1);
            ans[i] = tree->query(1, 1, x - 1);
        }
        return ans;
    }
};
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type Pair struct {
    val   int
    index int
}

var (
    tmp   []Pair
    count []int
)

func countSmaller(nums []int) []int {
    tmp, count = make([]Pair, len(nums)), make([]int, len(nums))
    array := make([]Pair, len(nums))
    for i, v := range nums {
        array[i] = Pair{val: v, index: i}
    }
    sorted(array, 0, len(array)-1)
    return count
}

func sorted(arr []Pair, low, high int) {
    if low >= high {
        return
    }
    mid := low + (high-low)/2
    sorted(arr, low, mid)
    sorted(arr, mid+1, high)
    merge(arr, low, mid, high)
}

func merge(arr []Pair, low, mid, high int) {
    left, right := low, mid+1
    idx := low
    for left <= mid && right <= high {
        if arr[left].val <= arr[right].val {
            count[arr[left].index] += right - mid - 1
            tmp[idx], left = arr[left], left+1
        } else {
            tmp[idx], right = arr[right], right+1
        }
        idx++
    }
    for left <= mid {
        count[arr[left].index] += right - mid - 1
        tmp[idx] = arr[left]
        idx, left = idx+1, left+1
    }
    for right <= high {
        tmp[idx] = arr[right]
        idx, right = idx+1, right+1
    }
    // ζŽ’εΊ
    for i := low; i <= high; i++ {
        arr[i] = tmp[i]
    }
}

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