Buggy python submission (verdict: Runtime Error):
# coding:utf-8

import sys

input = sys.stdin.readline
INF = float('inf')


def inpl(): return list(map(int, input().split()))


def show(X):
    for row in X:
        print(row)


def solve(N, M, info):
    distance = {}
    for L, R, D in info:
        if L not in distance.keys():
            distance[L] = {}
        if R in distance[L].keys():
            if D != distance[L][R]:
                return 'No'
            else:
                continue
        distance[L][R] = D

    for L, R, D in info:
        if L + 1 == R:
            continue
        if R - 1 not in distance[L].keys() or R not in distance[L + 1].keys():
            continue
        if distance[L][R - 1] + distance[L + 1][R] != D:
            break
    else:
        return 'Yes'
    return 'No'


N, M = inpl()
info = []
for i in range(M):
    L, R, D = inpl()
    if L > R:
        L, R = R, L
        D = -D
    info.append([L - 1, R - 1, D])

print(solve(N, M, info))


Fixed submission:
# coding:utf-8

import sys


input = sys.stdin.readline


def inpl(): return list(map(int, input().split()))


# ---
class UnionFind:
    __slots__ = ['nodes', 'weight']

    def __init__(self, size: int) -> None:
        self.nodes = [-1] * size
        self.weight = [0] * size

    # 検索
    def find(self, x: int) -> int:
        if self.nodes[x] < 0:
            return x
        else:
            parent = self.find(self.nodes[x])
            self.weight[x] += self.weight[self.nodes[x]]
            self.nodes[x] = parent
            return parent

    # 併合
    # def unite(self, x: int, y: int, w: int) -> bool:
    #     root_x = self.find(x)
    #     root_y = self.find(y)
    #     if root_x == root_y:
    #         return False
    #     else:
    #         rank_x = -self.nodes[root_x]
    #         rank_y = -self.nodes[root_y]
    #         if rank_x < rank_y:
    #             self.nodes[root_x] = root_y
    #             self.weight[root_x] = w - self.weight[y] - self.weight[x]
    #         else:
    #             self.nodes[root_y] = root_x
    #             self.weight[root_y] = w - self.weight[x] - self.weight[y]
    #
    #             if rank_x == rank_y:
    #                 self.nodes[root_x] += -1
    #
    #         return True

    # xとyのルートが等しい時: 入力された重みwが正しいかどうかを判定
    # xとyのルートが異なる時: xとyを併合する
    # True: 併合した，False: 何もしなかった，ValueError: 入力された重みに矛盾がある
    def relate(self, x: int, y: int, w: int) -> bool:
        root_x = self.find(x)
        root_y = self.find(y)
        if root_x == root_y:  # 入力された重みwに矛盾がないか判定
            # print(x, y, self.weight[x], self.weight[y], w)
            # print(self.get_tree())
            # print(self.weight)
            if self.weight[x] - self.weight[y] == w:
                return False
            raise ValueError
        else:
            rank_x = -self.nodes[root_x]
            rank_y = -self.nodes[root_y]
            if rank_x < rank_y:
                self.nodes[root_x] = root_y
                self.weight[root_x] = w + self.weight[y] - self.weight[x]
            else:
                self.nodes[root_y] = root_x
                self.weight[root_y] = -w + self.weight[x] - self.weight[y]

                if rank_x == rank_y:
                    self.nodes[root_x] += -1
            return True

    # UnionFind木の一覧を返す
    def get_tree(self) -> dict:
        tree = {}
        for i, node in enumerate(self.nodes):
            if node < 0:
                if i not in tree.keys():
                    tree[i] = []
            else:
                if self.find(node) in tree.keys():
                    tree[self.find(node)].append(i)
                else:
                    tree[self.find(node)] = [i]

        return tree


N, M = inpl()
uf = UnionFind(N)
relate = uf.relate
try:
    for i in range(M):
        l, r, d = inpl()
        relate(l - 1, r - 1, d)
    else:
        print('Yes')
except ValueError:
    print('No')

Buggy python submission (verdict: Runtime Error):
# coding:utf-8

import sys

input = sys.stdin.readline
INF = float('inf')


def inpl(): return list(map(int, input().split()))


def show(X):
    for row in X:
        print(row)


def solve(N, M, info):
    distance = {}
    for L, R, D in info:
        if L not in distance.keys():
            distance[L] = {}
        distance[L][R] = D
    for L, R, D in info:
        if L + 1 == R:
            continue
        if R - 1 not in distance[L].keys() or R not in distance[L + 1].keys():
            continue
        if distance[L][R - 1] + distance[L + 1][R] != D:
            break
    else:
        return 'Yes'
    return 'No'


N, M = inpl()
info = []
for i in range(M):
    L, R, D = inpl()
    if L > R:
        L, R = R, L
        D = -D
    info.append([L - 1, R - 1, D])

print(solve(N, M, info))


Fixed submission:
# coding:utf-8

import sys


input = sys.stdin.readline


def inpl(): return list(map(int, input().split()))


# ---
class UnionFind:
    __slots__ = ['nodes', 'weight']

    def __init__(self, size: int) -> None:
        self.nodes = [-1] * size
        self.weight = [0] * size

    # 検索
    def find(self, x: int) -> int:
        if self.nodes[x] < 0:
            return x
        else:
            parent = self.find(self.nodes[x])
            self.weight[x] += self.weight[self.nodes[x]]
            self.nodes[x] = parent
            return parent

    # 併合
    # def unite(self, x: int, y: int, w: int) -> bool:
    #     root_x = self.find(x)
    #     root_y = self.find(y)
    #     if root_x == root_y:
    #         return False
    #     else:
    #         rank_x = -self.nodes[root_x]
    #         rank_y = -self.nodes[root_y]
    #         if rank_x < rank_y:
    #             self.nodes[root_x] = root_y
    #             self.weight[root_x] = w - self.weight[y] - self.weight[x]
    #         else:
    #             self.nodes[root_y] = root_x
    #             self.weight[root_y] = w - self.weight[x] - self.weight[y]
    #
    #             if rank_x == rank_y:
    #                 self.nodes[root_x] += -1
    #
    #         return True

    # xとyのルートが等しい時: 入力された重みwが正しいかどうかを判定
    # xとyのルートが異なる時: xとyを併合する
    # True: 併合した，False: 何もしなかった，ValueError: 入力された重みに矛盾がある
    def relate(self, x: int, y: int, w: int) -> bool:
        root_x = self.find(x)
        root_y = self.find(y)
        if root_x == root_y:  # 入力された重みwに矛盾がないか判定
            # print(x, y, self.weight[x], self.weight[y], w)
            # print(self.get_tree())
            # print(self.weight)
            if self.weight[x] - self.weight[y] == w:
                return False
            raise ValueError
        else:
            rank_x = -self.nodes[root_x]
            rank_y = -self.nodes[root_y]
            if rank_x < rank_y:
                self.nodes[root_x] = root_y
                self.weight[root_x] = w + self.weight[y] - self.weight[x]
            else:
                self.nodes[root_y] = root_x
                self.weight[root_y] = -w + self.weight[x] - self.weight[y]

                if rank_x == rank_y:
                    self.nodes[root_x] += -1
            return True

    # UnionFind木の一覧を返す
    def get_tree(self) -> dict:
        tree = {}
        for i, node in enumerate(self.nodes):
            if node < 0:
                if i not in tree.keys():
                    tree[i] = []
            else:
                if self.find(node) in tree.keys():
                    tree[self.find(node)].append(i)
                else:
                    tree[self.find(node)] = [i]

        return tree


N, M = inpl()
uf = UnionFind(N)
relate = uf.relate
try:
    for i in range(M):
        l, r, d = inpl()
        relate(l - 1, r - 1, d)
    else:
        print('Yes')
except ValueError:
    print('No')

Buggy python submission (verdict: Time Limit Exceeded):
# coding:utf-8

import sys

input = sys.stdin.readline
INF = float('inf')


def inpl(): return list(map(int, input().split()))


def solve(N, M, info):
    distance = [[None] * N for _ in range(N)]
    for i in range(N):
        distance[i][i] = 0

    for L, R, D in info:
        distance[L][R] = D

    for L, R, D in info:
        if L + 1 == R:
            continue
        if distance[L][R - 1] is None or distance[L + 1][R] is None:
            continue
        if distance[L][R - 1] + distance[L + 1][R] != D:
            break
    else:
        return 'Yes'
    return 'No'


N, M = inpl()
info = []
for i in range(M):
    L, R, D = inpl()
    if L > R:
        L, R = R, L
        D = -D
    info.append([L - 1, R - 1, D])

print(solve(N, M, info))


Fixed submission:
# coding:utf-8

import sys


input = sys.stdin.readline


def inpl(): return list(map(int, input().split()))


# ---
class UnionFind:
    __slots__ = ['nodes', 'weight']

    def __init__(self, size: int) -> None:
        self.nodes = [-1] * size
        self.weight = [0] * size

    # 検索
    def find(self, x: int) -> int:
        if self.nodes[x] < 0:
            return x
        else:
            parent = self.find(self.nodes[x])
            self.weight[x] += self.weight[self.nodes[x]]
            self.nodes[x] = parent
            return parent

    # 併合
    # def unite(self, x: int, y: int, w: int) -> bool:
    #     root_x = self.find(x)
    #     root_y = self.find(y)
    #     if root_x == root_y:
    #         return False
    #     else:
    #         rank_x = -self.nodes[root_x]
    #         rank_y = -self.nodes[root_y]
    #         if rank_x < rank_y:
    #             self.nodes[root_x] = root_y
    #             self.weight[root_x] = w - self.weight[y] - self.weight[x]
    #         else:
    #             self.nodes[root_y] = root_x
    #             self.weight[root_y] = w - self.weight[x] - self.weight[y]
    #
    #             if rank_x == rank_y:
    #                 self.nodes[root_x] += -1
    #
    #         return True

    # xとyのルートが等しい時: 入力された重みwが正しいかどうかを判定
    # xとyのルートが異なる時: xとyを併合する
    # True: 併合した，False: 何もしなかった，ValueError: 入力された重みに矛盾がある
    def relate(self, x: int, y: int, w: int) -> bool:
        root_x = self.find(x)
        root_y = self.find(y)
        if root_x == root_y:  # 入力された重みwに矛盾がないか判定
            # print(x, y, self.weight[x], self.weight[y], w)
            # print(self.get_tree())
            # print(self.weight)
            if self.weight[x] - self.weight[y] == w:
                return False
            raise ValueError
        else:
            rank_x = -self.nodes[root_x]
            rank_y = -self.nodes[root_y]
            if rank_x < rank_y:
                self.nodes[root_x] = root_y
                self.weight[root_x] = w + self.weight[y] - self.weight[x]
            else:
                self.nodes[root_y] = root_x
                self.weight[root_y] = -w + self.weight[x] - self.weight[y]

                if rank_x == rank_y:
                    self.nodes[root_x] += -1
            return True

    # UnionFind木の一覧を返す
    def get_tree(self) -> dict:
        tree = {}
        for i, node in enumerate(self.nodes):
            if node < 0:
                if i not in tree.keys():
                    tree[i] = []
            else:
                if self.find(node) in tree.keys():
                    tree[self.find(node)].append(i)
                else:
                    tree[self.find(node)] = [i]

        return tree


N, M = inpl()
uf = UnionFind(N)
relate = uf.relate
try:
    for i in range(M):
        l, r, d = inpl()
        relate(l - 1, r - 1, d)
    else:
        print('Yes')
except ValueError:
    print('No')