Buggy python submission (verdict: Time Limit Exceeded):
import sys

sys.setrecursionlimit(10000)
INF = float('inf')


class WeightedUnionFind:
    def __init__(self, nodes):
        """
        :param collections.Iterable nodes:
        """
        self._parents = {k: k for k in nodes}
        self._ranks = {k: 0 for k in nodes}
        self._sizes = {k: 1 for k in nodes}
        # 直近の親からの重み。root なら 0
        self._weights = {k: 0 for k in nodes}

    def unite(self, x, y, w):
        """
        x が属する木と y が属する木を併合
        :param x:
        :param y:
        :param w: x と y の重みの差; (重み y) - (重み x)
        :return:
        """
        # それぞれの root をくっつけたいので root 間の重みに変換
        # x が上、y が下
        w += self.weight(x)
        w -= self.weight(y)

        x = self.find(x)
        y = self.find(y)
        if x == y:
            return

        # rank が小さい方が下
        if self._ranks[x] > self._ranks[y]:
            # x が root
            self._parents[y] = x
            self._sizes[x] += self._sizes[y]
            self._weights[x] = 0
            self._weights[y] = w
        else:
            # y が root
            self._parents[x] = y
            self._sizes[y] += self._sizes[x]
            self._weights[x] = -w
            self._weights[y] = 0
            if self._ranks[x] == self._ranks[y]:
                self._ranks[y] += 1

    def find(self, x):
        """
        x が属する木の root
        :param x:
        :return:
        """
        if self._parents[x] == x:
            return x
        root = self.find(self._parents[x])
        self._weights[x] += self._weights[self._parents[x]]
        self._parents[x] = root
        return root

    def size(self, x):
        """
        x が属する木のノード数
        :param x:
        :return:
        """
        return self._sizes[self.find(x)]

    def weight(self, x):
        """
        :param x:
        :return:
        """
        # 経路圧縮
        self.find(x)
        return self._weights[x]

    def diff(self, x, y):
        """
        (y の重み) - (x の重み)
        :param x:
        :param y:
        :return:
        """
        if self.find(x) == self.find(y):
            return self.weight(y) - self.weight(x)
        return float('inf')


N, M = list(map(int, input().split()))

uf = WeightedUnionFind([i + 1 for i in range(N)])
ok = True
for _ in range(M):
    l, r, d = list(map(int, input().split()))
    if uf.find(l) == uf.find(r) and uf.diff(l, r) != d:
        ok = False
        break
    uf.unite(l, r, d)

if ok:
    print('Yes')
else:
    print('No')


Fixed submission:
import sys
import time

sys.setrecursionlimit(10000)
INF = float('inf')


class WeightedUnionFind:
    def __init__(self, nodes):
        """
        :param collections.Iterable nodes:
        """
        self._parents = {k: k for k in nodes}
        self._ranks = {k: 0 for k in nodes}
        self._sizes = {k: 1 for k in nodes}
        # 直近の親からの重み。root なら 0
        self._weights = {k: 0 for k in nodes}

    def unite(self, x, y, w):
        """
        x が属する木と y が属する木を併合
        :param x:
        :param y:
        :param w: x と y の重みの差; (重み y) - (重み x)
        :return:
        """
        rx = self.find(x)
        ry = self.find(y)
        if rx == ry:
            return

        # rank が小さい方が下
        if self._ranks[rx] > self._ranks[ry]:
            # x が root
            self._parents[ry] = rx
            self._sizes[rx] += self._sizes[ry]
            # root 間の重みに変換
            self._weights[ry] = w + self._weights[x] - self._weights[y]
        else:
            # y が root
            self._parents[rx] = ry
            self._sizes[ry] += self._sizes[rx]
            # root 間の重みに変換
            self._weights[rx] = -w + self._weights[y] - self._weights[x]
            if self._ranks[rx] == self._ranks[ry]:
                self._ranks[ry] += 1

    def find(self, x):
        """
        x が属する木の root
        :param x:
        :return:
        """
        if self._parents[x] == x:
            return x
        root = self.find(self._parents[x])
        self._weights[x] += self._weights[self._parents[x]]
        self._parents[x] = root
        return root

    def size(self, x):
        """
        x が属する木のノード数
        :param x:
        :return:
        """
        return self._sizes[self.find(x)]

    def weight(self, x):
        """
        :param x:
        :return:
        """
        # 経路圧縮
        self.find(x)
        return self._weights[x]

    def diff(self, x, y):
        """
        (y の重み) - (x の重み)
        :param x:
        :param y:
        :return:
        """
        if self.find(x) == self.find(y):
            return self._weights[y] - self._weights[x]
        return float('inf')


N, M = list(map(int, input().split()))

uf = WeightedUnionFind([i + 1 for i in range(N)])

ok = True
for _ in range(M):
    l, r, d = list(map(int, input().split()))
    if uf.find(l) == uf.find(r) and uf.diff(l, r) != d:
        ok = False
        break
    uf.unite(l, r, d)

if ok:
    print('Yes')
else:
    print('No')

Buggy python submission (verdict: Time Limit Exceeded):
import sys

sys.setrecursionlimit(10000)
INF = float('inf')


class WeightedUnionFind:
    def __init__(self, nodes):
        """
        :param collections.Iterable nodes:
        """
        self._parents = {k: k for k in nodes}
        self._ranks = {k: 0 for k in nodes}
        self._sizes = {k: 1 for k in nodes}
        # 直近の親からの重み。root なら 0
        self._weights = {k: 0 for k in nodes}

    def unite(self, x, y, w):
        """
        x が属する木と y が属する木を併合
        :param x:
        :param y:
        :param w: x と y の重みの差; (重み y) - (重み x)
        :return:
        """
        # それぞれの root をくっつけたいので root 間の重みに変換
        # x が上、y が下
        w += self.weight(x)
        w -= self.weight(y)

        x = self.find(x)
        y = self.find(y)
        if x == y:
            return

        # rank が小さい方が下
        if self._ranks[x] > self._ranks[y]:
            # x が root
            self._parents[y] = x
            self._sizes[x] += self._sizes[y]
            self._weights[x] = 0
            self._weights[y] = w
        else:
            # y が root
            self._parents[x] = y
            self._sizes[y] += self._sizes[x]
            self._weights[x] = -w
            self._weights[y] = 0
            if self._ranks[x] == self._ranks[y]:
                self._ranks[y] += 1

    def find(self, x):
        """
        x が属する木の root
        :param x:
        :return:
        """
        if self._parents[x] == x:
            return x
        root = self.find(self._parents[x])
        self._weights[x] += self._weights[self._parents[x]]
        self._parents[x] = root
        return root

    def size(self, x):
        """
        x が属する木のノード数
        :param x:
        :return:
        """
        return self._sizes[self.find(x)]

    def weight(self, x):
        """
        :param x:
        :return:
        """
        # 経路圧縮
        self.find(x)
        return self._weights[x]

    def diff(self, x, y):
        """
        (y の重み) - (x の重み)
        :param x:
        :param y:
        :return:
        """
        if self.find(x) == self.find(y):
            return self.weight(y) - self.weight(x)
        return float('inf')


N, M = list(map(int, input().split()))

uf = WeightedUnionFind([i + 1 for i in range(N)])
ok = True
for _ in range(M):
    l, r, d = list(map(int, input().split()))
    if uf.find(l) == uf.find(r) and uf.diff(l, r) != d:
        ok = False
        break
    uf.unite(l, r, d)

if ok:
    print('Yes')
else:
    print('No')


Fixed submission:
import sys
import time

sys.setrecursionlimit(10000)
INF = float('inf')


class WeightedUnionFind:
    def __init__(self, nodes):
        """
        :param collections.Iterable nodes:
        """
        self._parents = {k: k for k in nodes}
        self._ranks = {k: 0 for k in nodes}
        self._sizes = {k: 1 for k in nodes}
        # 直近の親からの重み。root なら 0
        self._weights = {k: 0 for k in nodes}

    def unite(self, x, y, w):
        """
        x が属する木と y が属する木を併合
        :param x:
        :param y:
        :param w: x と y の重みの差; (重み y) - (重み x)
        :return:
        """
        rx = self.find(x)
        ry = self.find(y)
        if rx == ry:
            return

        # rank が小さい方が下
        if self._ranks[rx] > self._ranks[ry]:
            # x が root
            self._parents[ry] = rx
            self._sizes[rx] += self._sizes[ry]
            # root 間の重みに変換
            self._weights[ry] = w + self._weights[x] - self._weights[y]
        else:
            # y が root
            self._parents[rx] = ry
            self._sizes[ry] += self._sizes[rx]
            # root 間の重みに変換
            self._weights[rx] = -w + self._weights[y] - self._weights[x]
            if self._ranks[rx] == self._ranks[ry]:
                self._ranks[ry] += 1

    def find(self, x):
        """
        x が属する木の root
        :param x:
        :return:
        """
        if self._parents[x] == x:
            return x
        root = self.find(self._parents[x])
        self._weights[x] += self._weights[self._parents[x]]
        self._parents[x] = root
        return root

    def size(self, x):
        """
        x が属する木のノード数
        :param x:
        :return:
        """
        return self._sizes[self.find(x)]

    def weight(self, x):
        """
        :param x:
        :return:
        """
        # 経路圧縮
        self.find(x)
        return self._weights[x]

    def diff(self, x, y):
        """
        (y の重み) - (x の重み)
        :param x:
        :param y:
        :return:
        """
        if self.find(x) == self.find(y):
            return self._weights[y] - self._weights[x]
        return float('inf')


N, M = list(map(int, input().split()))

uf = WeightedUnionFind([i + 1 for i in range(N)])

ok = True
for _ in range(M):
    l, r, d = list(map(int, input().split()))
    if uf.find(l) == uf.find(r) and uf.diff(l, r) != d:
        ok = False
        break
    uf.unite(l, r, d)

if ok:
    print('Yes')
else:
    print('No')